Hi. July 5th I Was Intimate W My Husband And

Hi. July 5th I was intimate w my husband and the condom broke. On the 6th I took the plan B and the next monday (13th) I got my period for a week. I didnt get my period in August but had a blood pregnancy test on the 13th and it was negative. I still have not gotten my period so now Im worried that I may be pregnant but late last night I had some red/brownish bleeding. Is this just old blood because the pill messed with my cycle or implantation even though it's been almost 2 months since that incident?