Am I bipolar or is it just diet?

My doctor says I have bipolar "traits" but not enough to say I actually have it. Here's my typical day: start out in good mood, but by 3rd period, my energy levels start to drop, leaving me feeling sort of down. Then I have lunch within an hour, but then I hit a low point around 5th period, an hour after lunch, where I get into that "afternoon nap" feeling. Then by 6th period, my levels start to climb back up. Could it be connected to diet and metabolism, or am I bipolar? It isn't a huge difference, but enough to affect my mood. also, I feel different on different days of the week. Monday I tend to feel great, but by Friday I'm exhausted