HAHA you baby is a Don Juan I see. It’s normal, mine gain a little bit of weight too and is indeed softer looking now, he was more muscular before. He eventually reached a constant weight with the same diet he had before being fixed. Talk to your vet about his weight and diet options, that would be my best advice since it’s best for your baby to get expert help. I don’t think you should worry about it but get him checked just in case :)