He might be trying to ween off
Whats his age?
Conures ween of at 2-4 months
Altho some can go as long as 6 months
Try offering him pellets veggies and grains
Maybe a bit of seeds as well
Raising baby parrots is not something to be taken lightly. One tool that will help enormously now and in the many years to come of parrot ownership is to have an accurate kitchen type scale and keep detailed records of his weight, amount of food taken in, how often, etc. Really really useful, as their weight reflects a lot about their food intake and general health. Decent scales can be had off of Amazon for as little as $19 plus a T-stand for him to perch on while being weighed. Should be able to read out in grams, among other weight data. Weigh at the same time every day and keep that record. I would say a loss of more than 10% of his weight is cause for alarm and should be accounted for. Baby parrots often loose a bit of weight as they transition to solid foods, so its important to be sure of things at this point. There is much more info available here on the ParrotForums on weaning baby parrots so make sure you search and read the available info on this topic.