Clomid dosage levels are determined based on the reason for the clomid to begin with. If you are not ovulating at all, a higher dosage may be given than to someone who ovulates on their own, just late. I have PCOS and am currently on 50 mg for the 2nd time. My RE didn't up my dosage because the 1st round I conceived, unfortunately it didn't work out beyond week 8. If we don't conceive this time around, then she will up my dosage. If you haven't had a cycle in over 2 years and even provera didn't kick start a cycle, then something more serious may be going on. If your doctor hasn't taken extra steps to find out what is wrong, I would seriously considering switching doctors or even investing in meeting with RE. Best of luck to you!
I have no idea how its decided what dosage of Clomid you take but docs normally start you off on eather 25mg or 50mg and work up accordingly if you dont ovulate, If you are put on Clomid your doc will monitor you closely to decide if it should be put up or even down due to overstimulation.
Speak to your GP about this and they will be able to put you on the dosage that will benefit you the most.
SSBD