Many women are going threw the same things as you they can help good luck
Sometimes thats how my periods start out. The first time it happened it scared me and I thought I was pregnant but I wasnt. Apparebtly its just old blood. Id say wait about a week. Within the week either youll have a full period or youll have only spotted a couple days and could retest to just see.
Ask in the am i pregnant forum
If you got three negatives then probably not. You can have your doctor test you just in case but its unlikely.