could be one of the reasons for irregularity in periods,so one advice is to remain stress free. Secondly get your thyroid
test done which might cause irregularity in periods.
For knowing your ovulation day we now have kits available ,these ae LH kits (i-sure kits) with simple urine test using this kit you would know when you ovulate.
Continue with your folic acid
tablets and don't worry everything would be fine.