Get him to a certified avian vet and at minimum, do a gram stain and blood-work.
It could be any number of things...2 weeks is unreasonable, as birds HIDE illness (as prey animals---showing weakness gets them killed in the wild).
What kind of baby-food, and does it contain citric acid? Too much citric acid can result in iron-elimination disease in birds (Some types are more prone to this than others)...Also, too much sugar, salt or protein can also be harmful to the liver etc (and some babyfood does contain salt etc).
Do you feed a mix of pellets and seeds?
Do you have a sleep-schedule for this bird?
Has he been tested for diseases such as polyoma, psittacosis etc?
Does he have any undigested food in his poop? How does his poop look in general?
How old is the bird?
Are you using any chemicals (candles, Teflon/ptfe/ptfoa, perfumes, air fresheners, cleaners, smoking etc) around the bird?
Do you notice tail-bobbing when the bird is perched and sitting still?