Can you get gas trapped under both sides of the rib cage? i get it on the left normally cos i have gastritis and ibs but lately ive been having hard-ish lumps under the right side, is that trapped gas also?

It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. It would be prudent to see a doctor. In the meantime, start exercising. Begin with low intensity exercise such as walking and gradually increase the intensity so that you sweat profusely. It may take a few months for the full effect. Wish you good health!