Maybe it is just getting older? I had hamsters, gerbils, rabbits, and Guinea Pigs growing up. The Guinea Pigs were sweetest - I think they would have worn sunglasses and designer threads, if allowed. :) Anyway, just a cut and paste:
"In the wild, the average mouse tends to live about five or six months. If living in ideal conditions, a mouse can live approximately two years. Ideal conditions for a mouse mean a steady supply of food without intense competition from other rodents or predators, as well as a somewhat temperate climate.
Mice can survive for months without water, getting the hydration they need from their food, or by licking the condensation from sink pipes. Reproduction slows down during periods of lower temperatures, so indoor populations breed throughout the year, while outdoor mice have peak breeding seasons during the spring and fall."