Chemical pregnancy?

Claire • 5 miscarriages, praying for my rainbow :(
So I got a BFP on Monday with a FRER, was very surprised as I was only 7DPO & the line was very clear! 
​I had some brown CM Monday & Tuesday, but other than that everything was fine! I tested again on Wednesday, just to be sure & the line had got darker! 
​So today I started having cramps, quite painful & now ive started bleeding, not heavy, but enough for me to know something is wrong! AF would be due on Monday so would I be right in thinking that I've had a chemical pregnancy? I've had 3 miscarriages last year, but it would seem that my body has found a new way to break my heart :( 
​I don't have any more tests, so will buy another tomorrow because I've read that they quickly turn negative when your having a chemical?