What Causes Persistent Spotting Triggered After Each Intercourse?

I've been lightly spotting for what seems like 2 weeks now. My cycle went off @ the beginning of the 2 week period and since then it seems like everytime I have intercourse it's triggered. It's never there when intercourse beginnings, but is always there afterwards. Idk what the issue cld be. I had my tubes tied after my last child and I am 27 yrs old. What can I do abt this situation? What cld be the cause?