I had a miscarriage 9months ago. i was 3months pregnant and had a dmc. we've been trying to get pregnant since and it isn't happening. any reasons why?

Many possibilities: If the D&C was routine and without any complications (like an infection or a perforation of uterus during the surgery) then it should have no effect on future fertility. How long did it take you to get pregnant the first time? You've had 9 months of not conceiving but you can't really count the month immediately after the D&C. If you reach one year without conceiving then you need evaluation.