My period has always been regular, very heavy during the first 3 to 4 days and lasts up to at least a week. My boyfriend and I had unprotected sex (about a week ago) around the 2nd day of my period and shortly after it had completely stopped. This is very unsuall for me because like I said it Lasts up to at least a week. I have been feeling very bloated for several days now. Almost like I need to stick out my stomach. I've also had slight pain in my lower belly? Could I be pregnant and how soon can I take a hpt to be sure?

Yes, of course you could be pregnant - your Pharmacist is the best source of info about which HPT to use and how soon.

Some women can and do get pregnant on their period... wait at least a couple weeks. (4 after the event) will get you a more accurate result.