Hi there welcome to the forum. I am sorry your little one is sick. Could you copy, paste and fill in the link and we can see if there is anything that we can help you with. As you have only had him for three days it is very possible he was sick before you bought him.
Your Chameleon- Yemen Chameleon, Male, 2 weeks old
Handling- Hes handled everyday (to be checked on)
Feeding- Size 3 crickets
Supplements- Exo terra calcium powder
Watering- Water is sprayed all over his cage
You are not giving us very much info . At two weeks old he should be eating fruit flys and pinhead crickets. Not sure how big size three crickets are. How often do you spray and for how long? Does your calcium supplement have d3 in it?
Giving d3 everyday will eventually kill your Cham. The shop is wrong. If that is the info you were given I wonder what other misinformation they have given you. I have given you a link to care sheets which will give you lots of info.https://www.chameleonforums.com/care/caresheets/
I would really like to help you more but the form you filled in is incomplete. It is very upsetting for you to see him ill as they are so tiny.
Some pet shops sell babies far too young. I have just handed over two babies that arrived at my local shop between Xmas and new year. I had never seen them so tiny. The shop were struggling with them, so I had them for three and a half months. They weren't eating but they were being given way to large insects . I managed to get them fruit flys, pinhead crickets and micro locusts and they were slow to pick up but they got there. Very small things in their environment can cause major problems as they are so sensitive. Your temps could be too high or too low. Their uv light could be too strong. I hope he picks up and please keep asking questions.