What’s happening to me?!

Okay so my husband and I have been TTC for 10 months, so I feel like I have a pretty good understanding of my cycles. My last period was March 21st and lasted 5 days which is normal, my periods are pretty regular. I was supposed to ovulate last week and still haven’t had a positive opk, but sometimes I ovulate later than predicted. I’ve been spotting brownish pink for the last two days (which is really weird), and again no positive opk. So I took a pregnancy test and it was negative. Today I feel like I have a ton of pressure on my lower abdomen. I just have no idea what is going on or what to think. Any ideas?