I have a Period question you might say?

So I have been having my period since I was 12 and Im 16 now. For about 2 years I been having irregular periods sometimes I wouldn't have them for 4-5 months but now I have been having regular periods and they are usually heavy. Put the "period" im having now is really light. its so light that hardly anything is on the pad. when i whip there is small amounts of blood. I guess im trying to ask is this normal? Its kind of freaking me out. Im not a virgin and im not showing any signs of pregnancy and i have taken a couple of pregnancy tests that are all ending up negative. I also am very careful when me and my partner have sex... Oh and I don't know if this is important but a couple of periods back I had a period that was mainly brown...