Horrible cramps and then a positive test?

I’m not pregnant. But recently I was remembering when I found out I was pregnant of my two children. It was the weirdest thing. The day of my period would come around and I’d get horrible burning cramps like I would during my periods at the time, no blood just cramps baddd, I’d wait til I completely miss the period window and then test and both times had a positive. When the second time happened I knew it because it was exactly like the first. But what on earth was that? I’ve never heard it happen to anyone else before, they usually just go “oh I just missed my period” then they find out but for me it was painful and then I wouldn’t get it again. It would legit happen right when I’m suppose to get my period. Has this happen to anyone else?