Dull pelvic pain

So... I know minds are powerful, and can play tricks on us.... But here's my story...

I started my digital opks on cycle day 10, received low fertility cycle 11 received low fertility..... Cycle day 12 peak! So I stopped testing. I skipped high fertility all together. I'm now on cycle day 21 and yesterday and today have had dull cramping in my lower abdomen. I think I need to wait until Wed to test. That will be CD 27 and the day of my supposed missed period. I'm also breastfeeding my son so my periods have been crazy. Would a uterus already be growing causing dull pains? :(