
If part of this was down to an upset digestive system, I'd go slow. Far better to let him come back to full condition at a sensible pace than try to stuff him full of food, and risk another dig.upset. My opinion
Males can look terrible when they've been around a bitch in season there's no doubt and it always seems to happen when you want them carrying decent weight for a show perhaps!! But again the fact he's around 2 could mean he still has some time yet before he is fully bodied up - especially if he comes from a slow-maturing line? One of mine was like that and I have no option but to put him away until he was over this phase. Which eventually he was and from just over 2 on, certainly looked the part. If you can be patient about all this, I would be rather than trying to force all this.
ps If he's being upset around the girls, as soon as you can, get them spayed!! It's what I did with our kennel - once retired the girls were spayed which was better for them too.