Scanty flow for 1. 5 days. No pregnancy?

Hello, I have started having reduced menstrual flow from 3 days to 1.5 days from past 2 years.. married since 2 years, trying to get pregnant since one year, but no success.. i had 4 failed iui's.. Can this reduced blood flow (including reduced shedding of utreus lining) have something to do with no pregnancy?? I m taking 2.5 mg letrozole since a year, and 2.5 mg letrozole + 3-75 units hmg injection since 4 months for iui.. With letrozole i used to have 6 to 7 mm endo lining and 1-2 mature follicle and with letrozole + hmg i used to get 9 to 10mm endo lining and 2 mature follicles.. Can i be facing utreus lining issue or what can be other reasons for me not getting pregnant. (Fyi... I have performed HSG test and my both tubes open)