I live by a junior high school, and today was such a beautiful day. So, I walked over to the track and briskly walked two laps and did 50 crunches. I am going to up this routine to walking miles each time, but I have felt so weak lately! I have never felt this tired in my life! Any suggestions? I think it is due to my lack of vitamins.

First off, good for you! Getting started is the hardest part of starting to exercise. Now you are on your way

In fact that's how I started off, fast walking - I did no crunches at first (I *still* hate stomach exercises!)

So to address your tiredness question: How long have you been LC? I see you just joined the forum. If it's only been a few days, give your body a little time to adjust to burning ketones from fat instead of blood sugar from carbs. It'll pass, and you'll feel great!

Way to go! I LOVE high school tracks - ideal place for any kind of exercises. It is easy to measure distance, ideal soft surface to protect legs, there are benches to leave water, sweat-shirt, usually there are water fountains, bathroom. Safe(r), clean(er)... The most important: outside:-)))Should I continue?
Our high school tracks are always very busy - dozens are walking, running, etc.
Feeling weak could be caused by lack of vitamins, or minerals - or many other reasons.
Calcium, magnesium, might help - usually they are sold in some kind of combination (sometimes with Zinc.) Potassium also.

I second IdahoSpud, if you started LC-ing a couple of days/weeks ago, it can be simply from your body adjusting for the new fuel:-)
Do not give up the walk, take it easy - you will see how fast your energy is back, even multiplies.