OOOOPS......if your cat is spraying a lot, then obviously it's not an obstruction. Sorry about that. It could still be urinary crystals or an infection, though.
I would still get your kitty to the vet to be on the safe side.
I agree w/ Sara! It could also be a urinary blockage (crystals).....especially, if it's a male. These obstructions can be life threatening in a short time.
Don't mean to scare you, but the cat needs to get to a vet ASAP!
Melly: I am not one of the resident cat experts but a hard belly is not a good sign. If it's a male and not neutered, he could be marking territory. OR it could be a Urinary Tract infection. Your vet would be the best one to ask. If it's behavior out of the ordinary, you should consult your vet.