Do you gutload your crickets? Gutloading your feeder insects are a very important part to feeding your chameleon, without gutloading them (esp bugs lower in nutrition such as crickets) it's similar to feeding your little guy potato chips. Also, chams prefer a varied diet so I would suggest getting a few other types of bugs such as dubia roaches, black soldier fly larvae, silkworms, locusts, etc.
I might reccomend getting him tested for parasites, esp since he's a brand new chameleon & showing signs that he may be unhealthy. Parasites are a pain to deal with, so it's better to be safe than sorry.
What are the dimensions of the enclosure?
It's extremely important to know the % of humidity in the enclosure as chameleons need high humidity levels, so you really should prioritize purchasing a hygrometer. & veileds specifically need 40-70% humidity.