How To Treat Persistent Pain In The Right Rib?

I have had right rib pain for the past two months that comes and go s a couple of weeks at a time. It is is tender to touch and very localised to a specific spot just either at the lowest rib or just under. No problems sleeping although does tend to be worse in the evenings and slightly better on waking in the morning. Hurts to touch or stretch too much. What could this be?