weird periods...

Ok...I normally have a very normal scheduled period. Usually around day 27-29. This last month was on day 30 which was a little werid. But even then the first day I didn't even have to wear a tampon. Which my periods are normally really heavy for about 7 days. (usually wearing a super plus the whole time). That night I was heavy and for two or three days I was heavy. Then after that I only had light brown discharge. For another three days. That was almost two weeks ago. Haven't had any more problems since then. Um.. Hadn't had sex since before my period with all the weird stuff going on. And had sex tonight, right after I started bleeding a very bright almost watered down pink colour.
I'm not sure what could be going on. We thought I might be pregnant so we took a pregnancy test a little after my period stoped. I'm going to hopefully see about maybe seeing a doctor or talking to a doctor tomorrow about it. But any ideas? Not sure what to do or what it could be. (Oh and the bleeding is enough to put in a tampon.)
Thanks.