Gina, you are of course right to check with a vet...and of course follow their advice, but I have had cats do this for several not very serious reasons.

1. they have been going a lot and the inside end of their tract is irratated. If the blood is bright red and on the outside of the poo, this is often the case.

2. they have what amounts to a cat hemeriod which bleeds on occassion...again bright red on the outside of the poo and the bleeding stops almost immediately after the b.m is done.

If the poo is all very dark, marbled throughout with blood or looks like coffeegrounds, there are more likely to be more serious issues going on than irratated tissues...

His playing, eating, etc. are good signs.

Good wishes....