Hi guys, I suffer from the exact same symptoms, I am 21 now and sadly I have been suffering from the same thing since I was 14. I have had tests for STI's and tests in my urine, along with seeing a specialist. The tests of my urine (which have been frequent over the years) have varied in results from positive to negative infection. Eventually my Urologist gave me 1 antibiotic a day for a month which sorted the problem out for 1 yr (which was a blessing!) However, the problem has come back, which was expected, and now I have the symptoms again.
I visited my doctor again today as when I am hot the symptoms get worse and I have been in spain for the past month (I do not know if you have the same response but heat + bikini's+ Chlorine makes the prob worse) but, just my luck, the burning stopped the day I visited the doc n no infection was found. It is common for you own body to fight the infection itself, if only for a few days.
Basically this is an extremely common problem, normally worse around a womens period or during 'bowell movement' as the doc put it. I was told today that sadly it is a problem that causes discomfort but basically results in women having to 'manage the problem.' Doing this requires you to recognise the triggers and take preventative measures. For example, for the past 7 yrs of my life I have got used to drinking at least 2 litres of water a day to take the edge off, my body almost reacts naturally to this now, when I feel a burn I feel thirsty.
Some women take 1 antibiotic everytime after intercourse, my other technique was litres of cranberry juice in a day! But don't take too many anti-biotics, as this is what causes more persistant and painful infections in the long run.
Don't panic about STI's, I did that and was shocked when it came back clear as I was convinced that was the cause, but if u r concerned, it really never hurts to check just in case, but everyone is very keen to pin everythin down to STI's in young women, which drives me nuts!
Hope this helps! I have scoured the internet, seen specialists and everyhting else, sometimes it is sorted and sometimes not, but sadly it is a case of just getting on with it and 'managing the problem' which after 7 yrs I have finally resolved myself 2, but it really isnt 2 bad when u get used to it.