alot of factors..the wind is always a factor the further ya go out. maybe yer tired...if ya dont shoot everyday, dont start now...ya gotta werk up to shooting 10 shots a day er ya could mess urself up.
a good anchor point is the key..i use the spot under my ear just above the jaw bone...you should be able to open and close ur mouth with out moving the knuckle.
could be the spine on yer arrows...the arrows dont fly straight, they wabble all the way to the target, so if its wabblin alot, it wont necessarily hit the same spot every time if its wabble is an inch er more.
always make sure your sights and rest are tight.