What Causes Clear Watery Discharge During A Period Along With Dizziness?

During my period it sometimes feels as though I bled trough but my tampon is not even full. It is just a clear watery fluid soaked that soaks onto my undies and sometimes clothing. I feel like I’ve always had poor digestion and either have diarrhea of constipation most of the time. I have been on birth control for a year now, and have regular periods. When I'm not on my period I do experience normal discharge for the most part, but during my period I've been experiencing this very watery fluid (currently on my period and this is happening). My periods are long and heavy but no cramps. I usually feel achy and somewhat sick during my period though. Lately, it sometimes burns when I have sex and/or pee (but not all the time). I clean myself everyday but sometimes my vaginal fluids have somewhat of a gross smell. I don’t know if it relates at all but I’ve been getting headaches more recently and my vision goes black and I get dizzy for a few seconds. I just went to the gyno for my yearly check –up but didn’t say anything because I didn’t see it as a problem then. She did the regular Pap test and checked everything and said I was healthy. No bad results came back or anything. I’m worried, and don’t know if something is wrong or not. Maybe an infection or worse? Help!