I had my period 10 days ago for 5 days and it was really heavy, then it was done and now i am spotting , and it really dark red. what could be wrong?

Usually nothing: Could you be pregnant? If not there are many reasons of ongoing spotting and heavier cycles; your cycle could have come late, you could have fibroids/polyps/endometriosis of the uterus. Do you use contraception? Sometimes this causes prolonged spotting. See your doc if it is ongoing (to r/u polyps and a thick lining in your uterus) and a thyroid test.