What Could Be The Cause Of A Bloated Belly In 20 Month Old Child With Pain And Weight Loss ?

Question : My 20 month old has had a swollen bloated belly for the last four months. When it started I took him in to his pediatrician because his belly button began poking out and it orginally went in. He told me to watch the bloating and note if it was accompanied by certain foods. Since that day it hasn't gone away his belly is just continuing to grow. He now looks like one of the kids you see in a 3rd world country with the bloated stomach and skinny arms and legs. Then after a case of bronchitis he began throwing up around 4 times a week. We have tried taking him off dairy which did not change the outcome. He has since lost two pounds since March. He went from 22.8 on March 5 down to 20.4 on XXXXXXX 1st. My pediatrician has scheduled an appointment for a month out to see what he does. I however am worried he is beginning to almost claw at his belly and cry. He has done this 4 times in the past month the only suggestion I get when I call is to feed him a bland diet. This doesn't seem to help. What could this be??? And what tests should I ask be done?