Chicks go through two juvenile molts before they get their adult feathers. They outgrow their baby feathers and have to replace them. At 3 months, he is probably going through his second and last juvenile molt. It is normal. He does not need anything except his regular feed.
Here are a couple of links that talk about molting. I think they have good information.
Sometimes when they molt they look bare. Here is a speckled sussex from last year.
Most are not anywhere near this rough looking when they molt. Especially with the juvenile molts, if I did not see a lot of feathers laying around I would not even know they were molting.