A protein shake isn't going to do much if you haven't eaten enough overall calories to build muscle. That's basically your problem. I would also switch out the full body workouts to something with heavy compound movements like deads, squats, military press, chess press and pullup/chinups....these always work pretty well for me and most of the people I know. You may also want to adjust carbs upward if your extremely low (under 100).......pretty difficult to build muscle otherwise, in my personal experience anyway.
Whether you think you can..... or you think you can't..... your 100 % correct.