Super confused

Kristine • Married May 10, 2014. We welcomed our baby boy into this world May 6, 2016!!!!!!
Has ANYONE seen anything like this?? 
It's kinda blowing my mind. 
This didn't happen to me but it just happened to my sister. Two days later (yesterday) she started what she thinks is her period. She is freaking out because now she believes she had a chemical pregnancy. Do y'all think she defied odds and happened to get a false positive or that she did actually lose a baby?? She went o urgent care and urine test said not pregnant but she also got a blood draw...haven't gotten the results back yet.