Good to hear that you’re in the process of making needed changes with lights, supplements, etc.
Being so young, he should probably have much smaller crickets/feeders than you’ll be able to get at most pet stores. I would suggest ordering some on line. There are some great vendors in the forum sponsors. I don’t think Josh’s frogs is a forum sponsor, but they are great for getting a variety of small feeders. I’m guessing that you may need 1/8 to 1/4” crickets/feeders for such a little one. It’s better for them to be too small than too big.
Low humidity can effect the eyes. Is your hygrometer analog or digital? The analog ones are notoriously inaccurate. If your hygrometer is accurate, perhaps adding an additional brief misting during the day may help raise humidity a little. The ideal range is between 30-50%, so you aren’t too far off. At night, you have a great temp drop and can use a cool mist humidifier to raise humidity. You don’t want to use a humidifier during the day as high heat plus high humidity increases risk for respiratory infection.
Basking temp should come down a little to 80. The best way to do this is to raise the light off the screen top by a couple of inches. Little chameleons love to walk along the screen tops of their enclosures like little monkey lizards, so you’d want to do this anyhow to prevent burns.
As your baby grows, he will need a much larger enclosure of a 2x2x4’ or equivalent.
Are you positive you have a boy? Male veileds will have prominent nubs on their back feet called tarsal spurs, which are visible even on babies.
Coming from Petco, there could be any number of things going on. He could have an internal parasite, supplementation was most likely wrong, etc etc or they could have just sold you a sick animal. The younger the chameleon, the less resources it has to fall back, on so even the smallest error in husbandry can be catastrophic. I would suggest a visit with a good vet (preferably experienced with chameleons) and a fecal check for parasites asap. Unless you luck out, you may have to travel a little bit for a vet. This will help you find one.
https://arav.site-ym.com/search/custom.asp?id=3661
I wish I had definitive answers to help you and your sweet little one.