Clomid 3-7 vs 5-9

I was prescribed clomid this is going on 4th round at 50 mg i do ovulate as to why i end up with af just not bfp so i was wondering should i maybe try days 3-7 or leave it at 5-9?? What is the difference if any??? I ovulate with clomid i just am not getting bfp and also what can i do to improve fertile cm as clomid dries me up ??? Suggestions, comments any help plz and thanks