Bleeding between periods.

Well first of all were have been ttc for almost a year and a half now. No luck so far. But in Feb I was suppose to start my period on the 9 I was a week late (which is pretty normal for me) then I started to bleed it was brown and light I figured it would get heavier th's next morning but it didn't. It lasted for a week and was never heavy. I took two test both were negative. I Did go to the Dr and had my thyroid checked and had my eggs checked everything is normal. And again yesterday I started light bleeding...idk what is going on with me. Anyone ever experience this?