When should I be worried?

So, my last period was February 15th. Usually my periods start anywhere between the 15th and the 19th. However, I didn't get my period the entire month of March. That only makes me technically 1 and half to two weeks late right? I have an appt with the ob/gyn on the 14th and hopefully everything straightens out by then. I haven't been sexually active in about 4-5 months (and always use condoms) so I highly doubt I can be pregnant. When should I worry? Because I'm stressing out pretty badly  and I'm terrified to take a test. Someone please ease my mind a little. Thanks. :)