Assuming 3.5 the relevant info is "A monk who selects this feat may attempt a stunning attack a number of times per day equal to her monk level, plus one more time per day for every four levels she has in classes other than monk."
So currently you get 3 uses per day, once you reach Monk 3/Fighter 4 you would get 4 uses per day.
also keep in mind that you can only use one stunning fist per round, regardless of level. from what i've seen that seems to get overlooked a lot and can create some pretty unfair situations.