Hi, ive had sex with my boyfriend and 3 days later i had a clotting period, could i still become pregnant?

Yes: If you've had unprotected sexual intercourse there is always a chance of pregnancy unless you've had a hysterectomy (removal - uterus). The chances are slim to none, but my recommendation is that you do a home pregnancy test 3 weeks after your bleeding stops - if it is negative you most likely didn't conceive from that sexual intercourse. You could also wait to see if you miss your next period