Vaginal Bleeding

Hello,

I recently turned 25 a couple of months ago and I realized that my menstral cycle is having some changes, for example i get dizzy and extremently irritateted before it starts. THIS IS MY ISSUE. I have a new boyfriend and we have been having sex since July. He is a little bigger than what I am used to and past boyfriends so for the first few times it was a little painful but no blood. In early Oct my cycle ended and a few days later we had sex and there was blood. This has happened after a cycle a few times so I did not think anythign of it. Well it has been a few weeks now it since then I bleed every time we  have sex, but not after sex (it does not run out like I am on my period), however I am used to his size now and there is no pain anymore. I went to have a pap smer and it was negative. I am wondering if this could be because if his size or if I shoudl have more test ran. I am also expecting my cycle to start again in a couple of days, so could this be related to a change in my cycle???