I had a miscarriage on 2/3. My doctor said my period would return in 4-6 weeks, but it has not. I'm not currently pregnant. Is there a problem?

Periods. It depends on what your periods were like before. If you are typically regular then your cycles should return to normal over time. If you were irregular then you will likely still be irregular. If you do not want to get pregnant right now then consider birth control for cycle regulation.