Failing finding another more obvious reason in your blood tests further down the line, if you are always worse and crash badly around 2pm it might be worth looking at your blood sugar levels or something you are eating?
Blood sugar levels are easy to test with a cheap testing kit from the pharmacy. If they turn out to be less than favourable, you can eat different things to help this.
It turned out most of my issues since childhood were actually down to eating gluten. This would make me tired all day all the time regardless and had sleep disorder anyway and never felt like eating much or got hungry but it was definitely always worse in the two hours after eating and would literally fall asleep on my desk. I would often skip breakfast or grab banana etc and then have a sandwich or something at work, then crash. if I skipped lunch, I could even get through the day a little easier sometimes although this is obviously not a great thing to do lol. You could try eliminating the two obvious ones dairy/gluten one at a time to see if changes anything or failing that, you could try a complete six week elimination diet to determine if you notice any improvements with the removal of other things.
Good luck in figuring it out, just keep looking for clues and ruling things out