Sore abdomen at 36 weeks?

I’m 36+4 and my entire stomach area feels sore, like every time I cough or yawn or sneeze or shift positions it just feels generally sore. What could this mean? I have had issues with constipation so my doctor told me to take Miralax every day and to drink one bottle of Magnesium Citrate, which I did yesterday. Could the laxatives be making my abdomen feel sore? Or could it be sore from straining on the toilet? Or could the soreness be labor pains?