Ovulation on letrozole

Has anyone had a dosage of letrozole work one month and not the next? I got my dose increased last month from 5mg to 7.5mg, and I ovulated for the first time and had a few follicules 20+ but this month I didn’t have any follicles above 7 😞 What were your next steps? Stay at that dosage and try again next month? Different meds? This is our 5th cycle and I’m starting to feel so discouraged. I guess I just got my hopes up way to high after last month.