4 days late

I have pcos My periods have been somewhat regular for 2 years since I started metformin but the lengths of them vary. But I always have spotting and bleeding randomly in between. This time I have had nothing and I am 4 days late. Its odd for me not to have any spotting at all between periods. My question is when should I take a test? Also I took a cheap dollar test one day before my period was late and it was neg. Help? Confused