2 rounds of Clomid

Have any of you ladies have a dosage of Clomid NOT work and was prescribed the same dosage again and it worked the second time .? (If that makes sense)  currently on my second cycle of 50 mg Clomid which I don't think worked by doctor making me try same dosage again . Had chemical pregnancy back in December with no help of Clomid. Does that make a difference that I sometimes ovulate on my own .?