In am so sorry your baby had this.
It was most likely an abscessed anal sac:
Apply warm compresses and then neosporen to keep him comfortable,
As long as it does not swell up again he should be fine. If it does he will require an oral antibiotic from his vet.
Feed him soft food for the net two days.
Please let me know how he is feeling. I hope he will be fine.
Warmest best wishes,
Dont worry about paying more - as long as your baby is ok,that is reward enough for me!
Thanks for your accept.
sending as an info request so you are not charged again!