I'm afraid I disagree with the above poster who said that you're being an idiot and that walking etc. alone can't cause you to lose weight. I think it's a bit of a vicious cycle. In my second year I walked miles and miles most days (3 mile round trip to campus, 2/3 trips most days, occasionally more) and I lost dangerous amounts of weight. I got down to almost 8 stone and I'm a 5'11" girl!
Firstly, I think it might simply be down to the fact that spending so much time in transit every day means you genuinely have less time to eat, or to think about eating. Secondly, I find exercise can make you less hungry, and also when you're tired at the end of the day it's easy to sleep rather than eat. Thirdly, as you've realised, the less you eat the less you want to eat. After an eye-opening trip to the doctor when they wouldn't let me leave until they were satisfied I wasn't hiding some kind of food disorder I realised that what I'd been convincing myself was an adequate meal, and indeed, exactly the quantity of food I'd always eaten, really wasn't. I told my flatmates and they were great at keeping an eye on my portion sizes, insisting I helped finish off leftovers even if I wasn't hungry, things like that.
I also slowed down my walking pace and treated going to campus as a relaxing activity, not a race to see how fast I could power walk a mile and a half (I always ran late!)
Try things like smoothies - really quite calorific if you have one a day but you won't feel like you're overloading your system with junk. Easy to get down, too, if food's making you feel sick. And if you buy cartons you won't even have to smell/prepare anything before you eat it. Simple things like putting one more spoonful than you think you need on your plate will help. And definitely tell people who see you eating/eat with you. They're probably a better judge of your weight/how much food you're REALLY eating than you are.
Good luck! And it'll probably all sort itself out when you relax during uni holidays!