Thanks for writing to the forum!
Lower right abdomen pain is commonly due to appendicitis. The pain, can at times come and go and not give the classic picture. Crohn’s disease, diverticulitis, infection in kidney, kidney stones, constipation, and an abscess in rectus abdominis muscle or psoas muscle can all cause lower right abdomen pain. Ectopic pregnancy, cysts of the ovary, extra uterine endometriosis too should be looked into.
Three possibilities come to my mind; chronic involvement of appendix (many a times ultrasound misses this as the appendix in such cases is hidden behind loops of intestine and typical symptoms of appendicitis are absent), involvement of kidney and inflammation of your intestine.
If you have a past history of surgery, then the pain could be due to adhesions. Diagnosis is only by laparotomy.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!