How many tries with Clomid?

I have been on Clomid for 5 cycles now. I did 2 at 50mg, didn't ovulate either time. 2 cycles at 100mg, ovulated the first time, not the second and my doctor just upped my dosage to 150mg, just finished taking them. My cycle is very irregular. My concern is that all of the paperwork that I have been given with the Clomid says that you should only take it for 3 cycles. But my doctor doesn't seem to think there is any problem with me continuing it. How many cycles of Clomid is too many?