If you think you are about two weeks pregnant and had a once off heavy bleeding and the pregnancy test showsis positive does that mean you had a miscarriage?

It is possible, but the bleeding could also have been from implantation bleeding. A pregnancy test will show positive for a while after a miscarriage because your body has not rid itself of the HCG (pregnancy hormone) levels yet. The further along you were, the longer a pregnancy test will show positive. I would still be on the lookout for any symptoms of pregnancy, continue taking your prenatal vitamins (or at least folic acid), refrain from alcohol and tobacco and caffeine then in a couple weeks take another test and see. Or you can go to the doctor to either confirm pregnancy or miscarriage.