This is a really tough situation. Only you know your hedgehog well enough to say if his quality of life is deteriorating. Think back to how he was a year ago and see if you notice any major changes. Sometimes they happen gradually so we don't see any day to day changes. A very wise friend of mine once told me when I was dealing with the same type of situation that it's better to let them go an hour to soon rather than a minute to late.
As for the not eating, after 5 days of eating very little he's not going to feel like eating even with antibiotics. You could try syringe feeding him if you can. He needs food in his system to stimulate his appetite. If it is to stressful for him then I would take it as a sign that he's getting tired.