Joseph, if you're hungry funny things can happen to you for no reason too!!
Look at it like that: our nerves (myelin sheath etc) are made of something - partly water, partly lipids (fatty substances), partly protein... If your body doesn't have the 'building blocks' necessary for your nerves and other system to function properly, funny things can happen!
Our bodies need food = proteins, fatty food, carbs, micronutrients like vitamins and minerals to function properly. If you don't give that to your body, hmm...?
If you are lacking magnesium or other important minerals/vitamins you can be more easily distressed too... It can also be hormonally related.. (And guess what? Hormones are made of something too!!)
It's usually a combination of factors: nutrition-related, maybe some environmental factors (like any chemicals in the air/exhaust fumes etc?) and maybe some 'hidden stress' from before (that you may not be aware of - either PTSD or stress that you think 'shouldn't matter'...) and then a little thing can 'push you over'...
For example, when I was a teen, I cried at school for a seemingly 'stupid' reason or 'no reason' - just for getting a 'bad part-grade' (not even a full grade).. But when I read the journal, I was amazed: our country was basically on the verge of war, my parents were totally stressed because of that and because maybe they would lose jobs etc. The stress was 'in the air' and so no wonder I 'snapped'... (we didn't eat so healthy either, and the chemical factory near-by was in one of the worst times, least regulated by law and some iffy things happened) So, it was a combination of factors. Sometimes it's easy to 'oversee' those... And think 'oh I should be happy, nothing bad happened' but if you look at the background, it can make more sense..
Like, recently, the whole world was under stress because of what happened in Japan, there's the economic recession etc - and maybe seeing people that remind you of something can be 'the last straw'... And there are endocrine-disruptors (hormone disruptors) in many of our 'everyday objects', sometimes even in water etc.
So, there are BAD things and there are thoughts that can make a difference too.. If you keep thinking negatively of yourself or others, it can change your brain chemically too... CBT or good books can help..
What do you mean by 'aware of myself'? (Do you get thoughts like everyone is watching you and possibly thinking badly of you etc? This could be a factor.. The Step by Step program calls these thoughts 'ants' and 'lies' and it was very helpful to look at them like that!!) Can you also instead just look at other people's clothes or nature/park around you etc? Usually people are more preoccupied with themselves than others anyway!!
(There are books you can read that can help you change the attitude too!)
What you can do? Check nutrition - eat some BREAKFAST! (any breakfast is better than no breakfast, though again, check for any sensitivities/allergies.. and stay away from sugar and too much caffeine, hidden sugar too.. also stay away from artificial food additives if you can..) I know I was usually much more sensitive when hungry!
March an April are usually most stressful months for school, so imagine how RELAXED and relieved you'll be when it's over! And yeah, walking around snobbish or well-dressed/arrogant-looking teenagers can be kinda stressful too, but maybe they're even more insecure inside than you are!! (And just putting up a 'brave front'?! I know a few like that...)