You may have to try a different doctor who can run more tests, or it could be that your cycle is just changing and your menstrual cycle will start soon.
I'm sorry that I can't be of more help. A doctor is your best bet!
thats another thing i told my doctor & at the hospital too they both told me the test they ran on me were normal so idk what it could be..
Unfortunately, there are a number of things that can affect your cycle (ie, stress, medicine, illness, etc.). You are probably going to have to find out from the doctor what is going on in your particular case.
Good luck to you and Keep us posted! :)