I am having pain on my right side lower rib
Hello, I'm Dr. Branch, thanks for using Ask a Doctor. The pain you describe is highly suggestive of musculoskelatal pain, either involving the rib bone itself, or the cartilage, muscle, and ligaments between the ribs. While the most common cause would be strain from an activity or trauma that you may or may not remember, the description you give of being worse in the morning and getting better through the day suggests rheumatoid arthritis involvement, though this would be a rare manifestation. Rib pain can also rarely be caused by a rib fracture without a history of trauma, usually from another cause that is making your bones fragile.
If this pain just started less than a week ago, I would suggest continuing to treat it with the pain medications you have, try to rest, and see if it improves. If not, I would consider seeing your doctor to evaluate you for a flare of rheumatoid arthritis, and possibly being treated with steroids temporarily to calm the inflammation. If there is any concern of a rib fracture, a chest x-ray may be appropriate as well.
I hope that helps, please let me know if you have any questions about that and I would be glad to discuss it further with you.