If you didn't start your cycle within 10 days being off provera, you should have talked to your dr immediately becasuse that is not a good sign.
they need to do some bloodwork to see where your hormone levels are and if it looks like you are ether going to ovulate or have a bleed, they need to give you more provera for you to start the clomid.
3 weeks is way long. If you havent started with the provera than you couls take a blood test. I dought that you are pregnate but it is possible that the tests just arnt picking up the surge. Do you have PCOS? it sounds like you either need a stronger dosage of provera or something else is going on. Either way you need to see your obgyn or a specialist. Good luck! and keep us posted.