Spotting...pregnant or prolapsed bladder?

I had my tubes tied 7 years ago. My periods are normal and on time like clockwork! Every 30 days lasting 4 days only. My period came on Monday and stopped Thursday of last week. Went a full week of normal activities and had intercourse that Saturday after my period stopped. On Tuesday of this week, about 12 days after my period, I noticed I am spotting very light reddish brown blood. I have never had spotting before and I'm 35 years old with 3 kids. I was told at my gyn visit last year, my bladder was slightly prolapsed. So, my question is this...am I bleeding cause of my bladder issue or possible pregnancy or am i just going insane. Figured I'd ask here till I see my Dr next week. I've never had spotting after periods before and i did have sex the Saturday before I spotted, but why did I not bleed sooner? Just randomn questions girls lol.