5 days late, 2 Negative PT

So I had a baby about 8 months ago and the week after PP bleeding stopped, my period returned. (About 2-3 weeks after birth) The problem is that I used to be completely regular (perfect 29 days in between, 3 days bleeding and one day of light spotting) and now my periods are all over the place. They are super heavy for 2 days, "normal" flow for 2 days, one day of light bleeding, and one day of light spotting. That part is "regular" but I literally can not even properly track it anymore because I go from 28 days to 33 days etc. The app is literally never right like it used to be before I got pregnant.

Well, today I went to Dollar Tree and bought 3 tests. 2 Negative, the other I'm saving to take either in a few days if AF still doesn't show up, or just keep it for future purposes. Now, I'm just wondering if I should have bought a First Response Test or something. But tbh, I found out before with both of my kids on pee sticks from save a lot. So, I'm just wondering if someone else has some insight. I remember my periods going back to normal after having my first child. And honestly, I don't think I'm pregnant. I just have that feeling that I'm not. Maybe I just really, really don't want to be. I'm not sure at this point. I just wanted to see if anyone could think of another reason for my period being so late (other than pregnancy, obviously, or normal things like stress, exercise, lifestyle changes, etc) and possibly a solution to make them regular again? I do not and will not use birth control anymore. (Haven't in 4 years)