Implantation Bleeding or Chemical pregnancy?

Kelly • Me: 26 DH:35 TTC#1 since Feb 2014
Hi! So here it is what is bothering me: a week ago, around 7dpo I had some spotting. It started with a drop of dark pink blood on TP, followed by 3 days of brown spotting, also only on TP that completely stopped at 10dpo. Yesterday at 12dpo I had a BFP. Wondfo was very very faint and FRER was clear. I am afraid to test again until AF is due (Wednesday) and get a BFN, in case I have had a chemical pregnancy. I was wondering if there are any difference between the spotting from CP and IB? Thanks Ladies! .