Oh dear, that does sound like one unhappy dog! I would guess that there are at least three separate issues here.
i. He's scared stiff of being sent away to the vets again, especially if he had an overnight stay there last week
ii. As he's still a youngster there's a bit of a power struggle going on and he's trying to assert himself as the top dog in his pack
iii. And of course he is still feeling lousy because of his illness.
Chances are your vet is right and he will settle down when he feels better, but of course if anyone in your family gets badly bitten in the mean time, that isn't going to help, and in fact will make your relationship with him worse. As you say, your mum showing fear is going to change the relationship dynamic for the worse.
I don't know what medication your dog is taking, but you could try asking your vet if he can have some kind of sedative to go with it. And can your medication be mixed in with something more palatable than bread, such as a piece of meat or his usual food?
I know of a brilliant holistic vet called Holly Mash (yes, that is her real name) who has a website and she might be able to advise on some kind of complementary therapy that might help him. Or consulting a dog behaviourist might help.
Try not to let him become 'top dog' in your household, otherwise this behaviour may well continue when he is better. Keep up with his usual routines and don't make too much of a fuss over him otherwise it could well develop into a permanent problem. In other words 'Keep calm and carry on!' as the saying goes. Good luck, and I hope he gets better soon.