My guitar can't hit high notes!?

ok, i can't remember how long its been happening but i know that i got the fender strat almost four years ago. when i bend a note on the high E string starting at the 14 fret, the sound/sustain becomes weaker, and when you bend it at 16 yo can't hold out the sound for even a second! this happens on all kinds of tones, rock, acoustic. and the gain can be at its highest and it wont work. now when i get a new pair of strings it only gets a little better and i mean LITTLE, so i don't think that is the problem, nor do i think its my playing, i have been playing for 6 years now. is it the guitar? or amp? the amp is a 10 or 15 watt fender amp that cam with it. i have played on other guitars and amps and can easily bend at the 19th fret. please help!