Pain in right side under belly 35 weeks pregnant?

Call YOUR OB NOW. Your OB knows u and your situation, could be a number of things some serious , some not but since u are 35 weeks no reason to take a chance, if u were my pt and u called this evening would send u to the labor room to be evaluated and make sure u and the baby are ok.
Likely muscular. Single sided pain along the front of your abdomen is likely muscular strain. Gently press on the area and see if you can reproduce the pain--if so, then likely muscular. If pain is more toward your back, must rule out kidney. If you have fever and/or bowel abnormalities, must rule out appendicitis.