MachTurtle

Hello KerbalSaver!  I use a joystick for both airplanes and spacecraft in KSP. The behavior you describe may be entirely normal depending on the craft and its situation. Above the atmosphere, control inputs use either RCS or control gyros to change the attitude of the craft and your inputs should allow you to point in any direction. In the atmosphere, however, control inputs probably use control surfaces (elevator, rudder, aileron, etc.).  Depending on the size, placement, and deflection of the control surfaces, your craft may be more or less responsive to inputs. Remember that the craft is (hopefully) designed to remain pointed in its direction of travel with no control inputs applied.  This is the quality of aerodynamic stability.  Usually, control surface deflections will allow your craft to point away from the direction of travel a few (5 - 20) degrees. Rudder will allow you to point left or right while elevator will allow up and down pointing.  In the atmosphere, this attitude change should allow you to climb, descend, or turn.  If a design is very stable, it won't be very maneuverable and vice versa.  If you want to increase maneuverability, you might try increasing the size or deflection of your control surfaces or moving the center of mass closer to the center of lift. Using SAS can affect maneuverability, so I usually refine my aircraft design without using SAS.
I hope this has been helpful. I'm sure other members can add to the discussion.  Happy landings!