Hi
Welcome to the MedHelp 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 (possibly missed on ultrasound), constipation, ovary involvement in women (cysts, hemorrhage, tumor, torsion-all ruled out in your case), ectopic pregnancy in women (ruled out), mesentry (a thin tissue that carries the blood, nerves and lymphatics for the intestine) involvement with low blood supply, enlarged lymphnodes, and an abscess in rectus abdominis muscle or psoas muscle (these two are unlikely is there is no localized patch of heat or lump) can all cause lower right abdomen pain. It can also be due to inguinal hernia (check this out as position wise it is a likely cause). Other than that at times pelvic inflammatory disease causes a lower abdominal pain along with a pelvic pain.
I think you should discuss these possibilities with your doctor. It is difficult to comment beyond this without examining. A comprehensive investigation is required keeping all the points in mind. Take care!
it coould be back pain. you may want to look into talking to a doctor because some of my groin pain is caused by my lower back pain. good luck