Hello. About 7 days ago, while lying down, I found a slightly smaller than a golf ball size hard mass right below my right rib cage. It has no pain & very slight tenderness. When I take a deep breath and hold it-i can feel the mass more than when standing or lying normally.

I am a little alarmed b/c i have felt a little bit more fatigue than usual lately. I'm not sure if this discovery and fatigue are linked emotionally, or? I have no health insurance and wondering if anyone has heard of such a thing? or if this is serious?
thank you for your insight.
I am a female, 30yrs. old. and have been completely healthy as of yet/never had any health issues or complications.