Welcome 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, ovary involvement in women, ectopic pregnancy in women, mesentry involvement, and an abscess in rectus abdominis muscle or psoas muscle can all cause lower right abdomen pain. An ultrasound or CT scan of abdomen will not be able to diagnose Crohn’s , diverticulitis etc.
Yes, it is possible for a spinal nerve compression to cause referred pain to the abdominal area. To know the cause a MRI would be required. The pain due to spinal causes that wakes up a person from sleep are generally due to ankylosing spondilytis or due to a tumor.
I would strongly recommend you to see a gastroenterologist (a specialist who looks after the diseases of our digestive system) and an orthopedic specialist. It is difficult to comment beyond this at this stage. Please let me know if there is any thing else and do keep me posted. Take care!