peeing during intercourse with my bf (read description 1st)

ive been with my bf a few months now.. we started off having sex pretty much everyday loads of times.. i had a fear of peeing but i knew that this was cos i dont let myself go and i finally let myself go cos i trust him 100% now i have to pee really badly as soon as we start (even if i pee before) this pee sensation is totally different to the peeing sensation i have when reaching orgasm. ive been to the doctors and all tests came back normal and i have also been for a check up at the clinic and im all normal.. i also tested myself to see if i will pee by doing it myself in my own room and i actually peed (after i had just been to the loo) i seriously need help with this as its causing my relationship  to die as its been 3 weeks since we done anything... im 20 years old and have been active for a long time so its not cos im new or dont trust him.. if there is anyone that could help me with this i would be so grateful as im done with being in and out of doctors to try and sort this. many thanks for the people that read this.. LJ