This sounds like it could be a combination of several things. After removing all of the training aids, did you recheck your C.G.? If not, maybe this could explain the change in your elevator sensitivity. It also sounds like one day you had a nice headwind to takeoff into, causing little yaw after liftoff, and more of a crosswind the next day causing more yaw after liftoff, but more importantly resulting in the need for more "groundspeed" to obtain the same "airspeed" as the day before to take off.