Hi Anandi
Sage here, when last have you had him outside? Also you need to know that you are lucky if you ever see your chameleon drink, i have only seen my Veiled drink a few times.
I would get him into the sun as soon as you can for at least 4 hours a day for the next week, it stimulates there appetite and everything.
My Veiled him self is on a bit of a hunger strike i have to chop and change the food to another insect every 3 days at the moment.
Get some meal worms +- 120 it has a yellow lid in the pet shop try it and let us know.
Just remember Veiled'z love to bask, getting him outside does wonders, but remember to mist him down if you see he turns very light or has his mouth open. Also make sure he has a little shad if it is really hot.
What enclosure is he currently in? Please attach a picture of his setup as soon as you can With the info and pictures we can help you make him happy in no time.