I started working out about 4 months ago at my local YMCA. I played Squash, exercised on the ellipticals and treadmills and did some occasional weight lifting. I went about 4 times a week for 2 hours each (1 hour moderate, 1 hour vigorous)

I am a petite girl, 5'4" and 106.2lbs. I know that I am "underweight" and my BMI is a bit "low" (I talked to my physician already) but lately, I've been pushing myself hard on the treadmills and ellipticals out of fear that I will gain lots of weight once I go back to school. I have a goal of reaching 105lbs by May 2nd (when my membership ends) and maintaining that weight throughout summer school.

I've also noticed lately that it is hard to concentrate on one thing. When my boyfriend talks to me, I often find myself drifting off into space and then suddenly snapping out of it and blurting something out, but I don't realize I've done this until after it's happened.

I've also noticed that lately, I've been feeling very tired and dull, and as a result I am taking lots of naps and waking up later than usual or sleeping in. I don't know if this is maybe because I have a very boring job... (?)

Not sure if all the above are related but just thought I'd mention them.

I guess I have a fear of exercising so much that it's becoming unhealthy, but at the same time I have a fear that not exercising will cause massive weight gain and inactivity. I'm also starting to count calories (eat less 500 and burn an extra 300) How can I find a healthy balance?

first of all think about what your doin, your underweight and if your cutting drastically you probably have malnutrition problems or you will get them so if the only reason your doin it is so you dont gain weight and become "unhealthy" your already ahead of the game because malnutrition is worse than an extra 5lbs of fat!!! Yes, your symptoms are all related, their mostly likely from either mantaining blood glucose problems, any number of vitamin deficiency problems (anemia i most common and iron deficiency), or stress/ and or depression. Your body is trying to give you all the signs to change your habits but your not listening. You should stick to a workout schedule, find your mantenance calories or at least a rough estimate(you could use the harris benedict equation), and slowly increase your calories up to mantenance and then a little over until you reach proper weight with the proper diet, if you do this to fast you will store it as fat because your body is probably already in starvation mode with your weight and height you are probably close to a 35% deficit which I wouldnt even recommend to someone who actually needed to lose weight. Change your lifestyle your body is tryin to warn you and if you dont you might obtain some bigger problems down the road that are easily avoidable, if you need any help or more advice dont be afraid to ask.

Beyond what the previous poster wrote, additional health risks of being underweight include osteoporosis and functional limitations (not being strong enough for common activities).

If you believe that you still have too much body fat despite being underweight (a condition often called "skinny fat"), then it is likely that a better remedy is to try to gain muscle. As the previous poster said, you may want to increase calorie intake to get back in balance, and shift your workout to increase the proportion of weight / resistance training to help build muscle. Your weight could increase, but if the increase is due to muscle instead of fat, that is a good thing.

IMO, I believe you should start eating "more healthy." I've read up on a lot about that and realized it makes sense. If you don't eat enough or don't eat healthily(preventing you from getting the right nutrients), you will feel fatigued and tired. I picked up a book called the Eat Clean Diet which is what pounded that idea into my head. I personally have experienced a boost of energy just from eating right. Eating right is the way to go.