The other problem I had was when my Minstrel degu had a respiratory illness. This is very common in degus and usually follows some kind of trauma or shock to them. I was advised by my vet to make a humidifier. We did this by getting a large Tupperware box, drilling a hole through it and placing a fish tank pump tube through the hole. We then pumped diluted pet disinfectant (see any reputable pet shop supplier) into the Tupperware and put Minstrel in for five mins a day to inhale the fumes and clear her lungs. Hold your degu close and see if you can hear it wheezing or struggling to breathe, if this is the case, humidifying may well be a positive course of action to take.
I’d also suggest you change its food and try some tempting sugar free treats. Try dandelion, broccoli or curly kale. Obviously anything sugary should be avoided but it may well be worth seeing if you can coax it back to eat with something really really tempting like a yoghurt drop and then switch back to non sugar when it starts eating again.
Good luck x