What Causes Pain And Pressure In Lower Pelvic Region?

I keep having lower pelvic/abdomen pain on the right side - maybe a couple of inches to the left of my right hip bone. They've done two ultrasounds and a mass is blocking them seeing my right ovary. They've taken blood today to check for cancer. It doesn't hurt every day or all the time. Sometimes it just feels like I want to push - as in having a baby. Could it be a blockage of some sort? Thanks!