Pantaleon - I know a gal your age who is dealing with this as well. You might want to check out the following website. It's very informative and answers questions in detail. The good news is that there are answers and it can get better. Hang in there.
Hi! I'm new here and would like to reply...I have vestibulitis and vulvodynia and this happens, especially when I feel a fatigue flare-up (although I've never been diagnosed officially...). Exams are the worst. Upon my first one, I jumped back so far that the doctor almost laughed at me and patronizingly asked "Have you ever had an exam before?" No, he wouldn't understand would he? Men... It was excruciating.
Also, most times sex is fine for me. But over the last few days, it has been very difficult for me. I get the burning you described. Sometimes I plow through it and after a bit, it's ok, not great, but tolerable, and I can enjoy it. Sometimes it's just impossible and I have to stop, ahem...mid-attempt. Right now I am having a very bad flare-up and believe that was the cause of the burning. I was also having UTI symptoms. It's getting better now.
It's hard to find a doctor who understands but they're out there so don't settle and don't give up.