Been there, done that. First, I'd say try to not be so insecure. You may not see it, but calling yourself "a barely-made-the-team struggling walk-on" isn't doing you any good. Do not put too much pressure on yourself. I used to do that and focus way too much on running, but in the long run (no pun intended), you need to define your priorities. As much as you enjoy running, it's not like you are being paid to be there.
The problem with running in college is that everything is squished into 4 years, all or nothing. Well there's a lot more time after college, so if you would like to continue to *enjoy* running and stay healthy, listen to yourself. You say you are tired all the time and do not perform well in races. A large part of that is because you are running too hard on easy days. I did this in high school and college, and did not realize it until it was too late.
What's funny is that the guys' team did not seem to have this problem as much. There were times that I ran with some of them on easy days and they went slower than the girls. The Kenyans ran even slower, both guys and girls. And of course they always kicked our asses in races and workouts. You would think that we would have caught on, but when you are in that environment, you want to run with your friends/teammates. It's easy to get sucked into paces that are too fast.