1 day period after 2nd iui?

Hi girls - wondering if anyone has had a similar experience:
I normally have very heavy periods that last 7 days (day 1 is generally light-medium, days 2-4 being heavy bleeding, the remaining days medium-light bleeding).
This is my second cycle of <a href="https://glowing.com/glow-fertility-program">IUI</a> with femara. This month I produced 2 follicles (1 was at 23, the other at 16) and had 2 IUIs (CDs 12 and 14), my OBGYN felt quite confident we'd be successful this cycle. I tested 11dpiui and 14 dpiui (counting from my 2nd <a href="https://glowing.com/glow-fertility-program">iui</a>), both negative. I got my period 14dpiui later in the day and had only about 1 day of heavy bleeding. Has anyone had this happen before? Thanks for reading!