Hello, Today Makes 9 Days Of Missed Period But Still

Hello, Today makes 9 days of missed period but still negative tests. I haven't tested in the passed 2-3 days. Anyway's I do not have any symptoms of even starting my period and my husband and have been trying. I already have a 2 year old. My question is when is a good time to do a test? If maybe my HCG is really low when could It pop up on a test? Or could this be something else?