Just my $0.02 -- when I first started Atkins, I had read (in the book and on this site) that most people feel really bad for the first few days, but then after that they feel great, so that's what I expected. But that wasn't exactly my experience.

I had very few problems the first few days of induction; mainly I struggled with caffeine withdrawl. As soon as that went away (maybe the third day?) I felt great. Then I remember crashing on Day 8. I was mad, like the diet had pulled a fast one on me. I posted something here saying "Why do I feel like crap? It's been 8 days, I should feel great now!" No one replied.

After a few more days I felt great again, and once I became accustomed to Atkins (and to the message boards) I realized that no one had responded because I had unrealistic expectations.

The first few weeks (possibly more than just the first two) you may have up days and down days. I think that's normal and it could be attributed to a variety of things. But if you can hang in there, you should see that overall you feel better than you did before and things like the afternoon blahs are much easier to manage than before low-carbing. So hang in there!