Mood Swing

I really get fed up with my mood swings. I've been feeling great for weeks now and today, despite waking up thinking about PC Sexy my mood has gradually become more gloomy. I am now sitting here with the sides of my mouth drooping and I don't know what to do. Over the last 4 days I have been missing going to the gym, yet, when it came time for me to do today I didn't want to go. When I got there I just felt tired and bored, though I did manage to stay for over an hour, I think that was more due to the fact that I was dragging my heels between machines than anything else. Even chatting to Nick didn't raise my spirits, he was there on a day off just for a work out and looked fantastic with his surprisingly hairy chest. I found out that he is 24 in April, so slightly older than I thought, but still far too young for me.
I need a pick-me-up but don't fancy going out drinking on my own. If I am in the same mood tomorrow morning I think I will treat myself to a shopping trip to see if that helps. I shouldn't really as my rent and ALL my other bills come out this weekend, but I need something.
I wonder if it could be caused by my poor diet when I am working. Because the client doesn't like us using the staff canteen (and I've seen the mice that live here), I take my own food in. Tesco is the only store that is open before I go to work and they have very little variety so I normally end up taking the same thing to work every day. I am not even able to use a fridge at work, because my food is likely to go missing if I do use one. Therefore my diet during work days is terrible, usually sandwiches, crisps, biscuits and sweets. When I get home I am normally too lethargic from doing nothing all day to be bothered to cook and so I just have something simple: pizza, microwave meal, soup. I wonder if eating like crap for 4 days is what ruins my mood (because of the wrong chemical intake from the food)?
Damn! I am so disappointed as I have been feeling so good lately, the best I have probably ever felt. It is so disappointing, which, of course, make my gloom even deeper!