Heath concerns 17 years old?

k so im 17 years old been suffering from mono, kidney infection, phenomena, kidney stones. Havent been to school 3 months. I started throwing everything up 2 weeks ago. I was told it was mono but was refereed to a gasterologist. They are giving me the mouth tube with a colonoscopy. They are biopsying a bunch of cells from my stomach and colon and lymph nodes. Why would they do this?>