Look at is as a learning lesson. When you start to get frustrated later, or think of giving up again, you can look back and remember how bad you feel now. You might even start a journal and write down all the things you want to go away, such as the aching knees. That way when you hit a stall you can look back and say "I'm still better off then I was then, and that means alot" It can be really motivating.