Implantation bleeding on the pill?

Someone help please, the past week I've been spotting and it's brown, I've been on the pill for 4 months and the only time I've missed it was by an hour and a half and I took it as soon as I found out, and this was about a month ago, I had unprotected sex about 2 weeks ago and I'm very sure that I'm not pregnant because I've been on birth control, but is this implantation bleeding?