If he’s in pain several days after his neuter, you should call your vet. Boys should be up and running within 2 days tops after a neuter. Pain after a couple of days means there could be inflammation or even an infection. Have you had a look at the surgical site?

In my opinion the vet ought to have given you pain meds. Since rabbits have the same type of sensory nerves and receptors and signal substances and brain pain-centers as humans, vets nowadays tend to go by assumption of pain after surgery.
Metacam is an anti inflammatory med that’s well tolerated by rabbits.

That said, the only natural remedies I can think of that might help him would be willow bark (and possibly willow leaves) and a heating pad to rest on. You can use a hot water bottle or handwarmers wrapped in a towel. It mustn’t get too hot of course. Just warm enough to take the edge off of the pain. But if there is inflammation or an infection in the wound, adding heat could make it worse, so please contact your vet first.

Hello and best wishes to Sully~~

You need to schedule a vet appointment to get pain medications, or at the very least, the your vet examine Sully. Meloxicam, a very common pain medication for rabbits, will not harm him in any way, and the most reported side effect is slight drowsiness for a little bit following administration. It’s low-risk as long as your vet weighs your rabbit and calculates the dosage accurately. Also, most rabbits love the taste of meloxicam, so giving it to him will probably be easy. Neutering is a fairly simple procedures, so having noticeable signs of pain days following the procedure is not a good sign. Sully may have irritated, damaged, and/or caused an infection at the sutures. All options need to be considered and evaluated by your rabbit-experienced vet.

Can you take a peek at his underside and see if there are any signs of swelling, redness, and general ill-signs? Also, how is his eating, activity level, and pooping?

If he is not eating, he needs to be force-fed Critical Care as soon as possible so he gets nutrients and does not suffer from malnutrition and starvation. Not drinking after a neuter is typical, but he’ll need to get water through wet veggies or being syringe fed water so he stays hydrated as well.