I know what you're going through. Right after the surgery my baby's head looked like half the size it was before surgery. He had an undescended testicle so the surgery was more invasive than a regular neuter. Make sure you keep him warm and comfortable. I cried when cocoster peed and pooped for the first time after the surgery (pee took about a day and poop took about 2 days). He had internal stitches too but my vet told me to discourage him from licking the stitches for 3 to 4 days. I made him wear a baby onesie overnight. Don't worry. He will feel better real soon.