Bruised lower back?

I'm 38.4 and my mom asked me what was wrong with my back she said it looked swollen. I'm a bigger person so I couldn't really tell if it was swelling or not but it does feel like there's some fluid in it but when I lifted my shirt we noticed that there's a purple tint to my skin it's like right over my spine. My back hasn't been hurting any more than it normally does I haven't noticed any other symptoms. My baby does like to always be in the back he has been for most of my pregnancy. My OB isn't open until Tuesday and I really would like to avoid an ER visit if possible because I haven't met my deductible yet and I don't think this is something I'd go to labor and delivery for because I'm not having contractions or anything. Just wondering if any of you ladies know what this is and if it's a normal pregnancy thing or not.