What happens when you take phentermine, but you eat some small portions of junk food?

I’ve been taking phentermine this is only for short period of time. I need to lose 20 lbs. Well it seems like im losing water weight more, and i get hungry at night more than I do during the day?…anyways when will do you think i’ll start seeing some results? because I’ve been taking it for a week and a half and I have seen nothing so far except that I just pee a lotttttt!