Problems with lethargy?

I was having issues were my energy levels would dip after lunch and never recover. My mood also seems to be very negative even if I have a great morning. Out of desperation I increased my caffeine intake significantly and I feel fantastic. Of course, I crash early evening since I don't want to take caffeine anywhere close to bedtime. I workout regularly, recent blood work came back normal and eat fairly healthy. I don't think this is depression since caffeine wouldn't affect my mood (as far as I know). What could be causing this? What are my best options for addressing this?