How to tell when ovulating

Ive been TTC for over a year. My OB put me on Metformin to help ovulate, and BC to hopefully get AF regular. I always feel naseuas, but all my test are BFN. I never can tell when Im ovulating because The ovulation tests saying no. So how can i tell personally? I just ended a period yesterday, when is the best time to try to conceive? My period tracker says my ovulation day is the 15th, is it lossible to ovulate sooner? Help!!