Missed period

Hi girls just a bit of help advice well I found out 18 months ago I have pcos! I was put on metformin witch has brought my period to 40 days apart 🙌🏼 I have been trying for my first baby but no joy as yet I’m about 7 weeks late now iv brought some cheap test of eBay and came back negative 👎 Sep one had the most Fante line water Mark iv done 3 other test and nothing so guessing it was a water mark after all has anyone had periods start ok on metformin then just stop 😤 Iv got a really heavy sort of feeling down below had it about 5 days now hoping I’ll come on or something 🙄 can pcos stop u getting a positive or medication as I do take meds for another problem I live in uk any help or best test ect to get or are they all just as good