Clomid TTC

My story- I am BFing. Haven't had my period yet. Dr prescribed Clomid 50mg bc I am TTC and have PCOS- took 3 rounds of clomid to conceive last time. I started Clomid on May 4. Got a positive ovulation test on May 17. But I haven't started my period yet and I had a BFN today. I have no clue when I am supposed to start. Is there a chance I won't? When could I start my second round of clomid??? Very confused.