yeah, definitely three months, at least. most people tend to give up after no more than two weeks because they aren't looking buff, but you really have to stick to it. i've been living healthy (dieting/lifting) for the past three years, and i seriously couldn't imagine myself NOT doing this for the rest of my life.
just make sure you STICK TO IT and be as strict to yourself as possible without getting sick of it. not sure else how to motivate you; you've just gotta believe in yourself. stay with it. for your own good. you truly will be amazed. i sure as hell was.