-try sleeping more. some people need lots of sleep. personally i don't recover well off anything less than 9 hours when i'm training a lot. some people are lucky and can get by on less, but maybe you aren't one of those people.
-get your blood checked. low iron is pretty common among runners, especially runners who feel like their fitness is lagging behind where it should be. low iron hurts running performance even before you reach the point where you're anemic.
-you may very well be overtraining. try running your workouts slower and running a bit less on recovery days. more mileage and faster workouts are good up to a certain point, but after that they only put you deeper in the hole. my coach in college always used to say that it's better to be 10% undertrained than even 1% overtrained.