How can I be pretty enough?

Hello, I have a girlfriend and I love her with all my heart but..I just wish I could be prettier. Or just gain a better figure. I want to please my girlfriend she loves me, I know she does and she tells me often but I think if I could be prettier she might be happier.. well actually I would be happier becuse then I wouldn't be so inhibited when I see other pretty girls. I don't have a jealousy problem (that has been proven from past experiences) anyway, sometimes she'll tell me about these pretty girls she sees in movies that she watches when she goes to the movies. I want to look good enough so she won't talk about them as often (not that she does it every time she watches a movie) its just..I would feel better about myself and my self esteem would go up if I could look pretty on the outside. I know that beauty is only skin deep..but Its nice when its on the outside too. I am 5 4" and weigh 139 pounds. I have larger hip bones but their isn't any fat there just bone. I don't have a large stomach but certainly not a thin one and my legs slightly touch together when I walk. I would like to know how to lose weight and how to keep it off. I am going on a trip for 3 weeks and I was wondering if I could be thinner by the time I get back? Thanks.