Bleeding and don't know why??

Kalee
Can some one help me???!!! I've had stomach pains for past three days and today I woke up to medium amount of blood. I'm confused as why because I had my period on May 1 -5. So what do you guys think I should do go to the doc or just let pass. This has happened to me before about 4 months ago also. Any one have a clue or guess as to why?? Thanks everyone