The issue might have been one thing at first that turned into another thing when you started trying to treat it with additives . I've often seen birds go off their food altogether due to the supplements (which won't treat illness anyway).
A change in vocalization with our birds is a symptom we can't ignore and I'll get a vet visit scheduled same week; when accompanied by lethargy (excessive sleeping) it's something I'd schedule within the next 24-48 hours.
Since your companion has been acting off for a while I'd get him seen no later than tomorrow.
It could be a relatively simple infection that would require a course of antibiotics (make sure your vet does a crop/vent swab and cultures, along with blood chemistry). The sooner seen, diagnosed and treated, the more efficient the recovery in most cases and ultimately the least costly.
One warning though, when giving antibiotics, give them meticulously and until they're all gone. Don't stop when the symptoms seem to be gone otherwise the problem is likely to return and be even worse than it was - and a lot more complicated to treat.
It's generally recommended that most of today's companion birds have a predominantly pelleted diet. Pellets have been continually updated since being introduced to the market years ago and today's formulas are better than ever.
Supplementing this diet with fresh foods every day is ideal and many owners find they can re-introduce seeds - in limited amounts (perhaps once or twice a week) without the bird refusing the pellets overall.
Even though the below link references 'cockatiels' it's applicable to your budgie too.
http://www.cockatiels.org/articles/nutrition/diet.html cites feeding both seed and pellets, but only after weaning from a mostly seed diet.
"Let's Talk Birds" http://www.letstalkbirds.com/cockatiels.htm ‘
The American Cockatiel Society http://www.acstiels.com/Articles/BasicCare/cockatie.htm
The Bird Care Library at Harmony Animal Hospital http://www.petvets.com/petcare/birds.html#nutrition
Good luck with your companion - and keep up the excellent observations. It's probably made all the difference!
I'm so glad to hear this. I knew by your question that you'd do the right thing. This bird should be with you a very long time. Stop back anytime you need anything.
God bless,
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