13 days late but test show negative

Jamie • Mon, Dec 08

I've been trying for almost 2yrs for #2 and I was put on Metformin last month. AF is 13 days late. I took a test on day 1 and another one on day 9 both being negative. My period is usually on time. Has anyone experienced this while taking Metformin? I know it's suppose to ell regulate you not screw everything up.