Period 2 weeks ago. stoped birth control bout 2 months ago. last night after sex started bleeding like a full blown period. could it be due to coming off bc , no itching , burn or pain , but read sti can cause bleedin trich,mgen,chl or would hav symp?

Chlamydia, gonorrhea and maybe M. genitalium can cause vaginal bleeding (but not trichomonas), but you are correct that having no other symptoms makes them less likely. Also, STI related bleeding usually is scant, not like a menstrual period. Any new or unexplained vaginal bleeding needs professional attention, so get care soon (including STI testing, since your question suggests you're at risk).