Experiencing pain around the lower bones

A couple days ago, I started experiencing pain around the lower bones in my right rib cage. The pain was most noticeable when I would press on that area of my rib cage. The pain wasn't bad at first, but after I left work, I started experiencing sharp pains that resembled that of a stitch, except it would last for several seconds. I went to the ER, where they did an ekg and a chest x-ray. The results from both came back normal, and the nurses told me it was chest wall pain caused by the muscles in my ribs, and that it would go away after several days. Now, two days later, I can press my fingers on that area of my ribs with very little pain. I haven't experienced anymore sharp pains, although there has been occasional minor pain that goes away rapidly. However, I'm concerned that this may have something to do with my gallbladder, liver, kidneys, etc. I'm 19 years old, and I don't think it's likely for there to be anything wrong, but I'm seriously considering getting an MRI to make 100% sure everything is ok. Is there anyone else who has experienced this, or who can offer advice on what to do? I'd really like to know why it happened so that if it is something serious, I can get it treated early on. Thanks!