This is typically a sign that the cat is uncomfortable about something. Just a possibility: kitty may not like the location of the litter box for some reason, or the cat litter itself feels annoying to it's paws. Sometimes a change in both location and cat litter will spark re-interest and everyone's happy again. Also, cats can be very sensitive to a change in YOUR mood or routine around the house, and express their anxiety in this way - not only can they be possessive about you, but also possessive about the way you are. When that changes, they feel a loss of their cherished old you. Anyway, the following litter made a huge difference to my troubled kitty...it's really great stuff - easy clumps to scoop, and holds odor really well. Cats like the feel of it on their paws, and like the special odor that keeps them going back. I highly recommend it! It's called Cat Attract:
http://www.preciouscat.com/ My neighborhood pet shop orders me the 40 lb. bags.
Good luck!
EDIT: Your frustration, overt or otherwise, will be sensed by kitty, and actually exacerbate the problem. Calm, caring detective work on your part is the
only thing that will give results. Take some time to regroup and bond with him affectionately and playfully. Our pets deserve only the very best, and are usually smarter and more sensitive than we are in many ways. They are our soul mates and loving caring guru's!