How do I get out of a slump from burn out?

I used to be a nationally ranked swimmer at age 13 and 14. I got mono and was out of swimming for a while. I came back and my performance has taken a real beating, and it's been two years already. I've been eating healthy, and getting rest. I practice 11 times a week with dry land each day and three and a half hours of swimming a day. I come to practice consistently. I'm burned out. How do I get out of my slump?