you don't know any girls who act weird? oh dear me. i bet every boy on the planet does.
people are generally weird and complicated. i think a lot of the problem is that we can't read each others minds and we think about stuff way too much, and read way too much into stuff, then use our wnderful imaginations to fill in the gaps in our knowledge and dabble with reality a bit.
you know whats weird? that you're all worried cos you haven't spoken since OMG yesterday!!!!1 i know its hard, but try your best to calm down.
thats not very long, really. a million boys would be bewildered by that one.
so maybe yesterday he was feeling a bit dopey or tired or distracted or unsociable or generally not chatty. maybe he's gone out today. maybe he was slightly overwhelmed by you showing up and saying hi and doesn't really know whats going on with that so has stepped back a bit to regroup. maybe he thinks he did or said something embarrassing that your failed to notice and is secretly cringing and kicking himself in his room. maybe you've started acting just a teeny weesy bit weird yourself and he's thinking "why do girls act so weird?" this very minute.
maybe just wait a bit and be cool and definately don't go spilling your guts in some bizzare rambly angsty email to him on on facebook (some girls have been known to do this sort of thing, not saying you would but erm... some of us *ahem* i mean them have. and it doesn't help at all with maintaining the fragile facade of not-crazy and the boys don't really know quite what to do with that and tend to quite wisely run away).
just chill. try not to think about it too much. you'll give yourself a headache and totally lose perspective and most likely get it wrong if you attempt to guess whats going on. just be normal, and the complexities of human interactions will become a bit more obvious and start to make sense soon ... like when you're 75 or so.