I don't want to eat anything at all. I feel sick sometimes. I lost interest in doing anything. Everything seems so boring and pointless. I also feel tired almost all the time. Probably because I ate only one chicken drumstick and a bag crisps in the last 3 days. I have no idea why I feel like this. I don't feel depressed though.

I've been in the same situation and its normal to go through these phases. I never felt depressed yet afterwards I realised that something in my life had changed that I wasn't happy with, I had just never figured out what it was. Seriously try to eat healthy (even though I know how hard that can be when you feel this way). The cause can sometimes be something in your system that's putting you off. And being healthy has the side effect of generally improving mood anyway. :D
Depression is what you're describing. It's not so much a feeling of sadness as it is a depression in your normal bodily function. *Nodnod.* Mmmpfh gives good advice.