What Causes Heavy Vaginal Bleeding Continuously With Clotting?

I have currently been bleeding for 13 day straight and it has been heavy compared to a normal period. There was some small clotting to.
I am currently on the pill and was not aware that I was pregnant and still don't know if I was.
I have been to the doctor who done a few tests. One of the tests she done on me was a blood test, the reason for this was because she found sugar in my water ( my mother had this when she was pregnant with me). She done this blood test to see if I had diabetes.
The test came back and said that the glucose in my blood was fine but would they still look to see if it was a miscarriage?
I have not had any other test back yet. Would a doctor be able to tell straight away if some one has had a miscarriage or could they miss this?
I have been very emotional recently and things are playing on my mind. I just want to know what is going on?