I have pretty regular periods and they are semi-heavy...

Last month I was like 3 days late but it was normal... but I started a week early this month and it started like in a brown color and it's just really light... I'm on my second day and it looks like when my nomal period is ending..

I don't think it's pregnancy because I haven't had sex since very early May and I've had regular normal periods since then except this month. I've taken 6 pregnancy tests since may until now and they have all come up negative.

Is having lighter periods normal? Or should I be worried?

Enjoy the light period. It may just be because you changed your birth control, diet, exercise or you have some stress in your life that can ultimately cause this. Nothing to be alarmed about, you don't sound like your pregnant, if you where you would know... I got pregnant this May and found out end of April so... that is not what is going on with you. Don't stress about it.