Very light period *tmi*

So recently I've been stressing out at the thought of pregnancy. I'm pretty sure I missed a period because I couldn't remember and I didn't log it in my calender (before glow), possible I could have just forgotten to mark it but anyways. I just started my period today....i think. I'm having normal cramps (terrible) but I've never ever bled this little before. I took a pregnancy test 3 days ago and it was negative but I said if i didn't get my period this week I was going to planned parenthood for a pregnancy test. I know you can have spotting during pregnancy and I'm just worried.