hmmm?

I will be 28 weeks tomorrow and for the last week or so I have been feeling this knot like pain in my belly... almost like there's gas trapped or I have to use the restroom. I'm almost certain it's not because I have to use the restroom since I've been going more than normal like twice a day. It's just very uncomfortable and Idk if it's a normal for this stage of pregnancy. I feel it at the top of my belly and lower part of my belly. I'm not sure if it could be pressure from the baby either? And also, is your back hurting something fierce?? I have to sleep with a heating pad every night to relieve this back pain. Please tell me I'm not the only one...?