Bartholin Gland Cyst?

Okay, I've had this problem before. After having a lot of sex/rough sex, my left side of my vagina gets really sore, it's always been the left and I feel like there's a small ball-bump there? It's not on the right, just the left. Every time I push the little ball bump, it's sore. I thought it was bartholin's cyst but I went to the doctor, they did some check and they laid me down, they didn't find nothing as I laid down. When I got back home, standing an d feeling it, it's still there but they can't see it as I lay down... It went away before but now it's back! Ugh HELP!