No menstruation :/

Ok so I am a bit worried since I haven't had my period for several months, let me explain: 
I did have sex with my boyfriend occasionally and didn't use any type of protection other than withdrawal. We are almost sure that he didn't cum in me. The last time I had a normal period was November, I skipped December and in January I had 5 days of spotting. In February, March and this month I haven't had a period. What could it be other than possibly a pregnancy (which I doubt because by now I would have felt other dramatic changes or symptoms)?????