Yes it is! And I notice you are female, please do not do what I see like 90% of the women at the gym I work at doing, which consists of running directly to the treadmill doing a light jog on it for 20-30 minutes, then getting on a bike for 15-20 minutes, then going and picking up some 5lb weights... that's what not to do! Haha
There are some really knowledgable women that post on this site, I'll leave the bulk of the advice up to them. But IMO get on a good weightlifting routine for actual strength training, a good cardio routine for fat burn, and you will begin to see results as well as some restoration to those terrible knees (which more often than not are due to a weakness of supporting muscles around the tendons).
As for diet, same thing, I'll leave it for the ladies, but IMO you probably need to cut down on carbs. Cut out the sweets and sodas to start with then start building up a more personalized diet for your goals.