Late periods. Tests were accurate?

I haven't got my period since 11 days. I got intimate with my bf(not sex) on 21st DECEMBER 2016. I had menses in JANUARY and FEBRUARY(3 days late). I took three pregnancy tests(last one on 10 weeks) and all of them came negative. But i keep having this fear I am pregnant. I am also having my exams rn and they are very important in my life. I Haven't got any symptoms except burping which stopped in between for a week but again started. I did not have sex with my boyfriend. Our genitals didn't touch directly. I had one layer of clothing covering my genital. There was no semen and my boyfriend says that there is very less probability that there was pre ejaculation. Am i worrying unnecessarily? I was also on 3 medicines incl. A multivitamin for 5 days but i stopped it 14 days ago. I am not pregnant right? All those pregnancy tests were accurate?