Im having another miscarriage/chemical!?!?

I just found out 4 days ago that I was pregnant I had 5 positive tests I missed my period and I woke up today bleeding with bad cramps 😢 but this is the 4th time this has happened to me in 1 1/2 years! Every time it was around my 6 weeks mark...the first 3 I was TTC and this one was an accident but why is this happening?!? I'm so confused and lost...I really want a 3rd child...I have had 2 healthy pregnancies so why can't I have another?