How often should I wear my retainer in order to keep my teeth straight?!

I got my braces taken off the other day and they gave me a wire retainer that I'm supposed to wear at all times for the next four months. However, I'm having trouble with it. It's extremely uncomfortable, I can hardly speak with it in because the plastic part that goes on the roof of my mouth is so thick, it's really such a ridiculous and awkward retainer. I can only wear it for small amounts of time. I tried only wearing it while I'm sleeping but it's so uncomfortable it keeps me awake. I don't want my teeth to go back. How often should I wear it (at a minimum) in order to keep my teeth straight?