Letrozole and bleeding mid cycle

Apple
Please help if you can! Hysteroscopy on 3/4 and everything went perfectly.  Started Letrozole 3/16. Dr said to have intercourse on 3/24. All ovulation tests negative at this point. Scheduled appointment to check size of eggs is on 3/25, and if all goes right then a IUI on 3/26. 
But now I'm bleeding. First it was light brown spotting like boogers for a few days. Dr said it would continue until "estrogen under control." Now it's gone from thick brown to now red/brown like just before a period. 
Has anyone had these issues? Should I call my doctor?  Please share. I'm worried and have been in tears about this. TTC for 2 years. 😔

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