My dragon tree is slowly wilting away, I don’t know what to do :(

Am I doing something wrong here? I had to repot him because my aunty overwatered him whilst I was on holiday and he shed SOO much. I water when the soil looks dry (and I check using a wooden chopstick). I’ve given him fertiliser once in the last month. He’s still browning and shedding. I guess the room may be a bit cold? And also there’s some white fluff on him where the leaves attach to the stem.

Any idea on what to do?