I gained a lot of weight and Im scared I wont be able to lose it all

you can definitely lose it all. count your calories, using something like caloriecounter.com which helps you keep track of what you need to eat and how much you've eaten already per day. as for getting back in shape, you have to take it slow. you said it hurts when you run, and that's probably because you are trying to do too much too soon. try just running a mile or two a day until you can do that comfortably, then start building up to the mileage you used to be doing. good luck!