Follicles stopped growing/shrunk

I recently had my cd 12 U/S and had a 14 mm follicle. We did a rescan 2 days later and it barely grew so we scheduled another rescan 2 days after that. That was cd16 and the leading follicle had actually shrunk some. Has this happened to anyone? What was your outcome? I was on letrozole 5mg for cd 4-8. I've already tried clomid and it didn't work for me either. What do you think the next step is as for as medicine for my next cycle?