How To Treat Pain In Lower Right Side Of Abdomen During Periods?

Pain on my right side.?Im female 15 and have started puberty already if that makes a difference. I have pain in my lower right side right where my leg hits my abdomen. I know its not a appendicitis because ive had this problem for too long. It really hurts especially when my bladder is full and only hurts more when i pee. Sometimes it hurts so much that i just have to curl up and sleep it off. I went in a long time ago and got a ultrasound but they didn't find anything. I have ignored it so far but it only gotten worse this summer- from hurting once or twice a month to hurting 2-5 days a week- and im tired of being in this pain. Can you help me?