Swimming is good!

I made my first trip to the Healthplex for swimming today and it felt really good. I thought they were closing at 2:30 but it was 2:00 instead. So I got in about 25 minutes of swimming before I had to get out. I really think that was enough for my first time of exercising since my injury because I was really tired when I finished. I have a lot of lost time to make up and to rebuild my endurance. However, using the walker can be exhausting too, especially if I have very far to walk. It's so hard to believe that I won't be able to get back out there with you guys until the day of the half marathon. It's so depressing to think about it that way. My last run was our first time to do 7 miles and I only did 6½ because of my knee pain. Even though the doctor told me I would have no problem completing the training for Chicago, how is it going to be possible? I don't want to give up but I keep asking myself if I'll really be able to do it. You guys will have doubled my 6½ miles by the time I can return to just walking. How can I do this?!