miscarriage questions

I had a miscarriage August 3rd and just took a clear blue yesterday that said 3+! About how far along do you have to be to get it to say 3+? And I also have been having a cramp on my left side the past few days. When I had a miscarriage my lower back was hurting bad and I felt like my uterus was about to fall out but I still can't help but worry 😭😭😭