What Causes Irregular Periods?

Hello. I am a 32 year old female. I have no children. I have been sexually active since around 16 years of age. And I have been on birth control up until April of 2010. After I stopped taking my pill I stopped getting a period. I went to see my ob/gyn and she gave me Provera for 10 days. I did get a period, that was in November and I have not gotten a period since. My husband and I would like to get pregnant some time later this year. One doctor wanted to immediately put me on Clomid, another doctor wanted me to have 3 ultrasounds and do saliva test to check my hormone levels. In your experience what could be the cause and is there anything I can do without expensive treatments?