Just as you have off days, or are more emotional at certain times, so too your GP may experience similar. She's human like everyone else. So if she seems hostile put it down to her having an 'off' day. But make a note of the day of the week and time of your appointment for future reference.
On next appointment, try starting the appointment by briefly asking her how her day has been going. You'll get a sense if she's stressed or not, before launching into your health issues. Also she might appreciate you asking her how she's doing, and so she'll mirror your attitude possibly for the rest of the appointment.
If hostility continues at that 2nd appointment, double check afterwards if appointment week day and time is similar to last appointment - if so, then something might go on with her on that day and time frame each week and so make a note to yourself never to make appointments around that time frame in future. If timing is different, then just note the day and week again.
On third appointment definitely pick a totally different day and time - maybe morning appointment. Might be a bit of an inconvenience for you, but she might be fresher and not so worn out. Start again by asking how she is doing before getting in your health issues. If hostility continues, then mirror her posture. So if her hands are folder, then fold yours, etc. Then once you are locked in similar position, slowly start to relax your body and position of hands, arms, etc. She will mostly likely subconsciously mimic you, and that may get her to relax.
One other thing, don't talk to her with arms folded or slouched. It's subconsciously picked up by the other person that you are close minded and stubborn. May or may not be true, but brain interprets it as a hostile position. I personally like to sit with my arms folded, because it warms up my hands, and didn't realise how this might be interpreted.
I'm aware of this stuff because I've been on negotiation training courses where they give body language tips on face to face negotiations. You can read some info about this here.
A couple of other tips:
if hostility continues on third visit, bring someone along with you next time as an advocate (e.g. your husband or close relative like sister/brother/mother/father). Just by having another person in the room, it might make GP a little more objective and less subjective. Also if you interpret hostility, you can ask the person with you afterwards if they interpreted similar or not from GP. You might find out their interpretation is different to yours, and because you trust them, you can talk openly with them about perceptions and maybe there's something you can communicate or think differently when with your GP in future. If they agree GP is hostile, then consider changing GPs - you are the consumer after all.
you might want to buy a voice recorder to bring with you to GP visit - assuming GP is OK with you recording the visit, then just switch it on during the visit. This is good for 2 reasons - (1) you can concentrate on the visit and asking questions without getting distracted about taking notes on her advice which you can listen to later on at your leisure, and (2) you can listen to the appointment at a later time to see if your impression of hostility holds or changes (after a cooling off period you might find she wasn't hostile but it was something you incorrectly latched onto during the appointment)
get comfortable with silence and use it to your advantage. Don't think you have to keep talking. Ask a question, and then just wait for the GP to answer. Sometimes they need 30-60 seconds or so to think and answer properly. Don't rush that, just sit quietly waiting. 30-60 seconds will seem like a long time but it is only a minute or less. If they ask a question to you and you need time to think it through then delay talking back until you've thought out your answer thoroughly in your mind, even if that means a bit of a delay when you answer.
Another I learned about only a few years ago, but it's extremely powerful and really simple. It's a male/female thing. Men tend to talk in 'you' statements. Women tend to say 'I' - problem with that is women tend say things like I have a problem, or I need help, etc. Subconsciously the other party interprets that as they don't own this issue or problem. But if you subtley turn your sentences into using 'you' then the other party will then subconsciously take ownership of the issue or find a solution. I read about this in a book about managing workload. I thought it was a bit of mumbo jumbo, but I was in a really desperate work overload situation with my boss so I decided to try it. We'd had several conversations before but nothing ever changed. What I did after reading that tip was outlined on paper all my work tasks, how many hours it would take to get them finished vs my normal work time, and then I handed the paper to my boss and asked 'what will you be doing about this?' The topic about my work and tasks was not new but the response was totally different just by tacking on that last 'you' question - the response I got from my boss was he would take away my information and come back to me with a solution. Two days later, he reassigned 25% of my work projects to someone else. Absolutely amazing! A couple of months later, my husband was having a problem with an unreasonable client who wanted more work done than what was originally agreed and without paying extra fees. I told him about this 'you' tip, and he did similar - he outlined the options which were basically to pay more for extra requests or stick to the original brief and original costs. He finished by asking 'what choice do you prefer' - the customer totally backed off and was much more reasonable after that. I now tell everyone if you have to complain, or you are in disagreement with someone, try not say statements with 'I' - flip it around to incorporate 'you'
Last tip - practice the conversation you plan to have with your GP ahead of time - think through possible couple of ways she might respond (both good and bad from your perspective), and then think through how you might respond to each of those responses. Just by visualising the conversation ahead of time in all it's various ways it might go, you'll feel more comfortable to handle whatever happens during the real appointment.