eh pigskin dont get mad at me saying this. but there could a few reasons on why you,re not getting it right
Number 1 : like what markedymark , dhalif and most of the guys are saying. maybe ur doing it the wrong way.
Number 2 , you,re practicing something outta your league. for example , learning to run before you walk
Number 3 : your long period of time actually isnt really long at all. I,ve been practicing tough stuff for over a year and still cant get it to fully sound nice and everything.
My advice. If its scenario 1. get some help find out what you,re doing wrong.
If ( i hope it isnt but theres always the possibility ) that its 2 or 3 then just practice even more and dont complain. After all , rome wasnt built in a day ya?
Peace.