What Causes Abdominal Cramps And Abnormal Menstruation?

Hi this is the second time in a row this has happened. The first week I think I m getting my period, it s spotting then it moves to bleeding only when I urinate which is normal color but has more clots. I m in this second week but the first time this happened I bled for almost 3 weeks. Also during this I occasionally get very painful abdominal pain. I am calling my doctor after the weekend but am very concerned if anyone can help until than. Thanks