Pains before bathroom?

I'm a FTM, and so far my pregnancy has been easy peasy! Up until this last trimester. I'm 31 weeks right now, and for the past 2 weeks, I get really bad cramp like pain in my lower pelvic/hip area, only on my left side before I have to use the bathroom(a #2). I don't even get the feeling of having to go anymore. I just know that I have to go because of the pain I get. It sometimes is so unbearable that I can't even get up or walk, but as soon as I use the bathroom, it usually goes away. As the days go by tho, it seems to be getting worse and worse and the cramping pain seems to be crawling now from my lower left hip area, up the left side of my back. I have an appointment this upcoming Monday, so I will bring it up, but has anything like this happened to anyone before?