Seeing as it was the bulb change that seemed to bring on the initial change then I'd suggest returning it back to how it was and see if that resolves it. However, on another note you say your hottest spot is 35c. This is not hot enough for a basking area, you are looking for a basking temp of between 41-45c.
It may not just be the bulb though, it could be one of many things. Possibly brumation, which could have been helped along by the cooler than needed temp you are providing but it could also be a sign of sickness. How is his pooing? You say he has a reduced appetite, how exactly? Is he eating veg? Does he looks hydrated?
Keep an eye on weight. Weight is the best indicator of a sick dragon, if he is simply brumating then he shouldn't loose much if any weight, significant weight loss would indicate ill health.
As suggested try reverting back to how it was before and increase your basking temp and see where this gets you.
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