Why do I always feel tired?

For the past 3 or 4 months I’ve just been feeling tired nearly constantly. I’ve always had trouble sleeping – off and on insomnia (self-diagnosed), but it didn’t cause me to feel exhausted. I wake up tired, my eyes feel heavy throughout the day, my muscles seem weak and ‘empty’. I eat well – very few processed foods, lots of vegetables, fruits, whole grains, beans, lean meats, eggs. I eat yogurt occasionally, but not milk or cheese. Can’t remember the last time I had candy or any sugared drink. No fruit juices, either. I exercise about 6 days a week, strength training and a jog/walk routine. Nowadays I have to pretty much force myself to exercise, and have had to greatly decrease my intensity, and slightly decrease my volume, of exercise in the past few months because I don’t have adequate energy. My endurance has dropped. My strength, as far as lifting, hasn’t changed much. I don’t feel like I recover well from exercise, either. Sometimes my heart rate seems too high, usually when I just wake up.
Now about my sleep. It’s not great. I can usually sleep well enough, but getting to sleep is my main problem. Often times I read for an hour plus until I’m tired enough. I try not to lie in bed if I can’t sleep, but instead get up and read or watch tv. I know I shouldn’t watch tv, but when I have trouble sleeping I get real panicky, and hearing the tv calms me a bit. I think it’s because I’m listening to people on tv, and I usually feel anxious at night because I feel lonely, to the point of panic. I’ve had anxiety problems before, a few panic attacks, one from not being able to fall asleep.
Maybe it’s my anxiety causing all the problems with sleep, but is the sleep deprivation the cause of my exhaustion?
Sometimes my thinking is foggy, and I have indifferent emotions and zero passion towards anything. I doubt I’m depressed – I’m not sad or feel hopeless. Yet I am starting to feel a bit hopeless about my fatigue. I decreased my exercise volume and intensity, thinking that was the problem, but it didn’t do anything.

Please give me some insight into this. I am 15, female. I take a multivitamin and drink enough water. Even with a few nights of 8 hours of sleep, I feel only a slight increase in energy. Do I just need more sleep? Can you give me any tips on how to get it, and with good quality? Any energy-boosting tips?