Never gotten a positive OPK

Laura
So this is my 2nd cycle on clomid. Last month I was on 50 mg and didn't ovulate. I took 100 mg this cycle, cd 3-7. I'm currently on cd15 and still no positive opk. I'm getting really discouraged. Has anyone else had a similar experience? What's next if clomid doesn't work for me? Thanks in advance for any input!