What is a reasonable dosage of Ativan?

My Dr perscribed .5mg, but i find it is doing absolutly nothing for me. I am 5'11 and weigh 275lbs. I woudl like to up the dosage so it will start chilling me out, but I dont want to go overboard. I did try taking 2 pills one time, and am not sure if I really felt anything or not.