Sore tummy

Hello im currently 28 weeks and in my third pregnancy.i wanted to know if any other mommas are experiencing what i am as i havent with the prior 2 pregnancies. I have a sore tummy. Its not like a stomach ache or something i ate didnt upset it . Its more like a workout kinda sore ..i find that when i sleep propped up or sleep sitting slighty up i tend to get it more . Its not a painful sensation but it is quite bothersome...anyone else experience this or know what this is ?