Blood streaked mucus vaginal discharge 4 dpo

I am a 32 yr old who has been trying to get pregnant for over a year since I got married. My periods are usually regular and my cycle lasts 26 days. On cycle day 18 for the past few years, I have noticed a large volume mucusy discharge with blood streaks, sometimes overall pinkish in nature. It often happens about 4 days post ovulation (by OPK's) and I use it as a signal for my pending period in one week. Pregnancy tests have been (-) through out.
After telling my doc, underwent an u/s that showed some fluid filled tubular structure but it did not look like my fallopian tube or ovary. Will go for repeat before my period next week.

Has anyone experienced this?

I know this was 2 years ago but just wondered what the outcome was? I have recently begun experiencing this every month. After a chemical preg. I worried it was early menopause even but stills eem to be ovulating and periods regular.
Would be great to have some info. I hope you got it sorted

anyone figure this out?