Weird cramping!!? Help!!

Hello everyone. Last night I started feeling a strong cramp in my lower left abdomen. I've never felt this before. When I lay on it or sit down the pain subsides. But when I stand up or walk it hurts badly! And this morning the pain was gone then it started back all over again tonight. :'( Why could this be happening? I'm not pregnant. I will go to the doctor but I just want to get some opinions first. I have attached a picture of my current cycle and AF due September 2nd. ​