Why Is My Cat Losing Weight And Pulling Its Fur Out?

Only your vet can tell you for sure. The only thing that can be said based on that is that your kitty needs diagnosis and treatment as soon as possible. Some options: Blockage, infection, illness, thyroid, or kidney trouble. Your kitty needs to be examined and some questions and details and history are needed before being able to narrow down the possibilities to figure out which diagnostics need to be done (if any) and what can be done to make your kitty better and/or more comfortable.