I second john's advice. you have to use the rest of your body, form a kinetic chain. But the problem is, once you get the rest of your body involved, you're adding a lot more power than you're probably used to. A lot of your shots are going pretty deep as it is. With added power, a lot of those shots are likely to sail long.
to counter that, make sure to:
--remove any lead tape on your racquet if you have any
--switch to 17g strings if you're using 16g
--tighten your strings, they may be a little loose
you'll get a lot more control with a tighter stringbed, more spin with smaller gauge strings. Extra lead gives you extra power, which you don't need.