I started meformin500 in may to lower testosterone and regulate periods. Got period in may. Now 10days late chance im pregnant or pills not working?

Both. If you are trying to conceive and your period is late, pregnancy is the first thing to check for. If the pregnancy test is negative, it may be that you will need to take the metformin for a few more months before your periods become regular.

It could be either.. It could be that the metformin isn't doing what you need or that you may in fact be pregnant. Consider seeing a board certified re sooner rather than later, as re's specialize in the diagnosis and treatment of pcos/ir.