What Causes Abnormal Menstrual Period With Bloating Of Stomach?

Days before my period my boyfriend and i tried to have sex but didnt because i can never take the pain. i am aware of that any contact of genitals can cause pregnancy. It felt like he had a pre ejaculation however those chances are quite slim i think. I am on birth control but that day i didnt take it on time. So when it is time for my period, i cramp just a little but nothing. I usually start on thursday morning Days before my period my boyfriend and i tried to have sex but didnt because i can never take the pain. i am aware of that any contact of genitals can cause pregnancy. It felt like he had a pre ejaculation however those chances are quite slim i think. I am on birth control but that day i didnt take it on time. So when it is time for my period, i cramp just a little but nothing. I usually start on thursday morning but i didnt start until late friday morning. And it started out extremely light then got heavier over the next few days. This is a very abmormal period for me. Since then my lower abdomin has been bloating/swelling. It decreases and increases at times though. So what could this mean? for me. Since then my lower abdomin has been bloating/swelling. It decreases and increases at times though. So what could this mean?