He's using his litter box an awful lot today. He's been in there five times in the past half hour. He seems fine otherwise - his behaviour is the same, he's eaten normally (wet food), he hasn't been vocal in the litter box but isn't very vocal anyway. It doesn't look like he is producing much urine if any.
He's 16 months old, neutered, otherwise happy and healthy. He's the only cat in the house. I can't see blood in the litter box. I can tell he's trying to pee but he doesn't seem to be straining much. Why does this happen on a weekend?! Should I call the emergency vet?