OTC Pill

Hey ladies, was wondering if anyone knew of anything over the counter I can take to bring on my period. I'm on Metformin and usually AF comes on time every month, but for some reason I didn't get it this month (no I'm not pregnant) anyways my doctor prescribed me something but unfortunately my insurance doesn't cover it and was wondering if anyone knew of anything I could take over the counter? Any advice I'd welcome. Thx ladies