Lump At The Bottom Of Left Rib Cage, Moves When Touched, No Pain, Fever, Severe Vertigo. Suggestions?

I've recently noticed this small lump at the bottom of my left rib cage. When I press on it slightly, I can feel it slide against my bone and move to the back. Once I let go, I can feel it automatically come back to the surface. It isn't visible through the skin though the area where it's located does seem to lift higher than the other side (the ribs on my right side). There's no pain but it's just really uncomfortable to feel something moving within my rib cage because I know it's not normal. I'm 20 years old and I noticed this lump about three months ago. Lately, about once a month, I'll get sick with a fever over 100 degrees and severe vertigo. I've also lost 15 pounds unexpectedly since everything started. I've made an appointment with the doctor but was wondering if anyone could tell me what it is.