Does metformin make you have false positive OPK's?

I have been taking JUST metformin 500mg 3 times a day for about 2 1/2 months now to regulate my cycles. I finally had a period that was brought on buy its self (with the help of the metformin) anyways i was wondering if while taking the metformin if it can give you a false postivie on OPK's. I have tested every morning and also some afternoons for the past 5 days with the postive line darker on some days then the others. My husband and I have BD on the thoses days.. I just dont know if i should belive the test or not. any help would be great....