This sounds like an odd situation. How sure are you that he hasnt eaten for 3 straight days? juveniles of that age usually eat a lot(the ones Ive had anyway) If hes not eating right, it may be a husbandry or stress problem.
Make sure hes getting all he needs. Humidity, heat, proper enclosure, stress level. All of these things have to be taken in account for a healthy chameleon. If you think youre doing all that needs to be done, dont hesitate to bring your little guy to the vet.
As for his underbelly, the best way for us or anyone to judge his to have it shown to us. Do you have a digital camera, if so take a picture and post it for us to see, many different angles is the best to make an acurent prognosis.
best of luck
and his underside is very dark. He now will not eat and just wants to sleep. its been 3 days and he hasnt eaten. too long for a youngen of only 3 months. Any creams? suggestions?
) I'd try to make a worm tray. Before I cup trained my cham I ended up cutting a milk jug, leaving the bottom and a back side. It turned out to be in an L shape, with a tray (the bottom of the jug) and a place for the worms to crawl on the side. I cut out a large area in the middle of the bottom and the side, and hot glued screen to cover the holes. This way, I could put worms in, but I didn't have to worry about them drowning when my mister went off. Also, the side encouraged my boy to eat seeing them crawl up and down the screen. Not very many got out, and I think the only reason one did was because I had to make one with elmers and masking tape before I got the hot glue. (It doesn't work very well. 
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