I had sex 3 days after my period ended & 4 days later my boobs became swollen/sore. they have been since then (week and a half) - could i be pregnant?

Maybe. Maybe not.: It can be hard to tell if a woman is pregnant because some of the symptoms seen in early pregnancy can also happen in non-pregnant women. A urine pregnancy test gives a reliable result if done correctly. One can test about 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period. An Ob-Gyn doctor can evaluate any persistent or worrisome symptoms.