I think you are right Mumof3girls about dehydration -> tiredness. Sometimes I struggled to drink at least good 1L ...especially when it's not so hot outside, or when I was working all day. I simply forgot to drink. Still, I kept telling myself that it was good for my skin and for health in general, but I just used to drink soda before I started Duromine and my weight loss plan and it was so difficult to change my habits at once. Drinking water too. So I got your point. Crappy and emotional feelings were common for me too, and maybe this was my body telling me that I needed water or more carbs (so I guess you are not wrong in your assumption), but usually tasty food helped me, and since I changed my diet I had to find some other source of positivity)).
I guess we just have to remind ourselves to drink water all day. You should definitely feel better then. I started with stickers, no joke. When I was at the office - there was a reminder sticker "Drink water" on my monitor. And it helped. After few weeks it became a habit, so I eventually took off the sticker and didn't need it anymore. There was a glass of water in front of me all day long, so I would be sipping during the day and take another one and so on. Although I can't really tell that I felt more awake because of water, since I was working full 8 hours. Btw, if you feel like a headache that may be the signal to drink more water as well. It's all about habit I believe.
On the other hand, your tiredness could be caused by something else... We don't know your day regimen.