Implantation bleeding 13 days post ovulation????

My husband and i started trying to conceive this past month. I have read alot about conceiving and pregnancy symptoms and implantation and realize that it is quite uncommon. We had unprotected sex at the right times in my cycle and waited patiently for my period. The day before my period was due i had brown discharge, i was disappointed and told him i got my period, had a little cry and got ready to try again. The discharge lasted for 2 days and then nothing? My periods are very regular and always start on the 28th day of my cycle, they start in the morning with cramps and blood and within the next couple of days flow heavier and then back to nothing by the 5th day. It has now been two days since the discharge stopped and I am wondering if anybody has ever had anything like this happen and actually be pregnant? Has anybody had implantation bleeding 13 days post ovulation?