Brown blood this morning! I thought I was 7 wks!!!??.

Yasemin • Married to wonderful hubby! Have two gorgeous girls 16 and 9. Trying for number 3.
I had my AF September 4-8 when it didn't come in October I tested 3 times and I got BFP. This morning when I went pee brown blood came out into the toilet and it was brown on the TP. I didn't really have any symptoms besides low back pain and mild cramping, sore boobs. This Thursday was supposed to be my first doctors appointment ?. I've had irregular cycles before ranges from 23-38 days. I've even missed months but I always tested and it was always negative. What is happening??? I was soooo excited that after almost a year of trying I thought I was finally pregnant.  Can anyone just tell me what could have happened???please I need some support. Thank you!