You know your bird better than anyone here if you feel something is wrong there is something wrong do not second ques yourself often times that can be to late. I would say like mentioned some blood work and some investigation of if he got into something he should not or ingested something . Is he a shreader and do you have rope toys in his cage? check all toys if he ingested some string from toy it can inpact in his digestive tract and cause him not to eat. Check his poop and describe it it should have round green color stool (round coil shape) and white mostly color Uratres . I put white copy paper at bottom of cage so I can observe my birds poop from time to time.BUT I would go to vet's anyways and get blood work describe to vet poop color and keep a eye and make sure he is eating..rr