Workout recovery for over 60

I swim about 1600-2000 meters (short course) a couple of times a week, sometimes three. I'm looking for advice on how to improve my recovery. While I'm working out I feel great, but after, and for a good 24 hours after, I feel completely wiped out. I find it difficult to sleep after a workout (takes the form of waking up a lot during the night), which feels so counter-intuitive if I'm so spent and feeling good about it. 

I have never taken vitamins or supplements, only because I've never felt I needed to. But I figure I must be nutritionally deficient in something. I'd like to improve these recovery periods. Any advice?