Losing Motivation

Hi guys! My name is Theresa and I began my weightloss journey last July and I was doing so well until about November. I had lost 30 pounds and was getting to that point where my clothes were starting to fit and I was feeling GREAT! But then an old knee injury came back to haunt me. I gained about 10 pounds back and now I can't do anything "high impact" such as running, jumping, or even a lot of walking. The elliptical is ok but I haven't really tried much else. Ever since then I might go to the Y (YMCA) once a week and can't bring myself to do much else as far as exercise. I still am watching what I eat and watching my calorie intake which I feel good about, but other than that I haven't been doing much. How to I find my motivation again?? :( HELP!