What Causes Stomach Pain Along With Constipation And Nausea?

I've been having stomach pain on the left side near my navel, constipation, and nauseous but havent gotten sick yet. It's b
een almost 2 months and been getting worse. I've been to the doctor twice and they have no clue what

it could be after 2 ct scans, x rays, bloodtests, and ultra sounds. Do you know what might be causing my pain? I'm only 15 and I dont know what to do.
Thank you