Does irregular periods mean ovulation problem? I had miscarriage 3months ago still waiting for 2nd period. What is the problem?

It could but. In general irregular periods mean inconsistent ovulation. Three months after a miscarriage might be too early to make any long term judgements. If you desire pregnancy then tack your cycles over the next 3-4 months and bring the calendar in to your doctor. If you do not desire pregnancy then schedule a visit for birth control to prevent pregnancy and provide cycle control.
Possibly. It can take 4-6 weeks from a miscarriage to have a first period. Periods should be regular thereafter. If not, it may indicate a hormone imbalance that warrants investigating.