Abdominal Solid Mass on upper left quadrant

I am 18 years old. I found out I had gerd about 3 years ago. Recently, I have had this mass on my abdomen right below my left ribcage for about a 7-9 months so far. Maybe even a year. I went to see a doctor and the doctor tried to take it out but missed it. I got an MRI done and nothing showed up but they did find a cyst on or in my kidney that is about 2 inches big. Since the lump did not show up, I got an ultrasound done and they say its a solid mass and that I need to get it taken out. I also have one showing up on my right side below my rib cage also. I don't know if this is related but I have had horrible back pain and I get tingly toes in the morning when I step down from my bed.
  What could cause this lump and what could it be?