Your cat definitely needs the vet for a diagnosis, but the combination of yowling, litter box problem and restlessness sounds like kidney disease and parahyperthyroidism, which often occur together (the second a consequence of the first). Kidney disease can't be reversed and by the time of diagnosis, a cat will have lost an alarming percentage of kidney function, but they can get by on just 5-8% and the condition can be alleviated by a range of treatments depending on the stage and symptoms, so don't give up right away--. Excellent information here: Here