When to test? Answers please!

❤TTC #1🤰🏽❤
My last day taking metformin will be March 3. (I take 500 mg 2x a day) My OB thinks I'll be pregnant by April, if not she's gonna prescribe clomid. Of course a missed period could mean nothing with PCOS. Any suggestions on when to test for a BFP after taking metformin?