Hi there! Welcome to Pet Talk!

Your bird sounds like a sweetie!!! At 4 months, he could possibly be going through hormonal changes, or getting ready for his first molt. These changes could possibly be causing changes in his behavior. I would ask the vet if you're concerned. I have never had this issue with my birds.

As to the food issue, birds are often picky with new foods. Be consistent, and keep offering him those fruits and veggies. Hopefully, with time, he'll come to love them.

Ps. I'd love to see pictures of your sweetie.