Ovulation is normally around 14 days before your next period. If your cycles are not regular (and even if they are regular) you have to chart your fertility signs (mainly basal body temperature) or use an ovulation test to determine when the best time will be. You can search the web for 'natural family planning' (NFP) and 'fertility charting'.

Women very seldom ovulate during menstruation as you will have an extremely short cycle that way.

Best of luck with conceiving!