How do I tell my girlfriend.....?

I am living with my girlfriend, and I have had the same problems as you. But, they are now gone. The way I did it was encouraging her to exercise and if she wouldn't, then a couple days later i would tell her I liked the way some clothing item looked on another girl and say that you think it would look good on your girlfriend. Maybe it will convince her to go out shopping and she will want to be in shape and care more about self appearance. I dont know if that will work for you, but it did for me and not my girlfriend is not lazy at all! Good luck!