Brown discharge day after sex

I am almost 7 months postpartum, and every time I have sex or an orgasm, I get a brown discharge mixed with egg white cervical mucus the day after. It has happened to me 4 times this month.

I also have had yellowish/green tinted discharge since I gave birth. Have had been tested for a variety of things four times now with all test results saying I am good. I have been on antibiotics three times to see if it was BV and my symptoms did not change.

What could this be? Or could this be related to my hormones? And why could I be having the brown blood the day after sex?

I have been to two different OBGYNS over this and they both act like I’m overreacting