Kim, I don't have much advice to offer, except I can confirm that most people do get sleepier in the afternoon. I think it's when your body temperature is at its highest or something like that. I gave up studying when I was in school for late afternoons because I would always fall asleep. Something active I could do, but not read or anything like that. So you are not abnormal. And knowing a couple of people who work for Social Security, the only thing I can add is that they tell me that the more documentation they have, the better and easier it will be.
Good luck!
Sue Ann