I noticed a spot of blood in my kitten's litter box?

I have a 5 month old kitten that got neutered about 4 days ago. He has healed up really well. He's eating and drinking normally and is acting like his usual self. The other day he started peeing frequently and in small amounts and now he seems to peeing as normal and he hasn't yowled or strained when goes.

However, I noticed a bright red spot of blood in his litter today. Wondering how serious this is considering he's acting normal. The cost of the neuter was covered by the rescue & he's not a patient with them so when I spoke to them on the phone they said it's not related to the neuter and might be stress related or could be a UTI. The vet is pretty far from me so it would be diffcult for me to get there and my sister thinks I'm being dramatic.

Advice?