Quote Originally Posted by Freedom
That is usually the main sign of a UTI - urinary tract infection or a blockage. And a vet visit is in order asap, as those get life threatening really quickly.
freedom hit the nail on the head. I've heard of symptoms of a blockage being described as frequent trips to the litter box with nothing comming out. I've also heard of people mistaking constipation for a urinary tract infection or blockage. If it is something extremely serious like that I'd say get the cat to a vet immediately.