My periods is three days late and irregular. What to do?

Hi doctor,

I am trying to conceive. My periods have been irregular for years and never come on time. I am using an application to calculate my cycle as best as I can. I should have ovulated on 7th and my period should have started on 26th, however it did not. Yesterday, when I wiped there was a stringy, slimy discharge tinged with orange and I started getting mild cramps not quite as strong as menstrual cramps. Yesterday was the only day I have seen this type of discharge and it happened twice and was gone. Then today I noticed a brown kind of discharge that then turned to a light pink and red color. I have just spotted a little, which are not enough for a tampon or a pad and not enough to really fill a panty liner. I have seen a few small clots, but not many at all and the cramps are still very mild.

Normally when my period starts it will start as spotting for the first hour or so and then pick up and it is always heavy and dark red. I have never had this before. According to the app, I used to calculate my periods. My period is now three days late. Again, they are irregular and I never know when I will have them. I took a home pregnancy test yesterday and it came back negative. I did have unprotected intercourse a few days before I was supposed to ovulate and on the day of ovulation. At first I thought it was implantation bleeding, but now I am not sure. I do have the Rh factor and I am Rh negative. I had a RhoGAM shot when pregnant and now my daughter is 19 months old. I had a miscarriage before 5 years. My nipples were really sore a few days ago and I woke up with sudden nausea the same day but nothing since then. Any help or insight would help a lot. Thanks in advance.