Are you touching down on the runway straight and not drifting? On a paved runway, if you're not fairly aligned and drift free, the plane will do two things, swerve and if it's enough of a drift, it will hop. This is the first skill to master, and since you can't see straight ahead on landing, you have to be good at using your peripheral(diagnal left and right front sides of the nose) references to judge drift and yaw on touchdown. If you're using only one side to judge your alignment, chances are you're yawed away from the centerline somewhat as you touch down. Use both peripheral references and compare them to remain aligned and centered. If you have the impression that you should be "wings level" and crabbing on touchdown instead of slipping for crosswind, your landings just aren't going to work out that well.Secondly, learn the 3 point attitude and altitude. Sit in the plane and learn exactly where the horizon should be relative to your peripheral references. Altitude is judged based on the apparent geometry of the runway edge lines. THE RUNWAY EDGE LINES If you know you're above the runway and not at 3 point attitude but sinking, then you can do something about it - slight flare. If you know you're at 3 point attitude and sinking, you can maintain the 3 point attitude and add power or just flare a little bit more. If you're pitched above 3 point attitude and ballooning, you can deal with it. The goal touch down softly at the 3 point attitude, so you have to be controlling the descent rate precisely as the plane slows down. That means a soft landing with power off will always require increasing angle of attack at the instant of touchdown. The rate of increase of angle of attack depends on the rate of deceleration and rate of descent. You have to be very precise with the pitch increase at touchdown because it's easy to balloon if you pitch too quickly too soon.
From what you described though, I think the problem is alignment with the runway or drift. You're probably only looking out one side of the nose and touching down in a crab or a drift (one and the same thing as far as the forces that will act on the airplane are concerned). Make sure you use both left and right peripheral references to judge your straightness and drift. Do some low passes on a long runway to get the feel for it.
Just so you know, it doesn't matter if you're in a Stinson 108, A Cessna 170, a Pitts S2B or an Extra 300, landing sideways will cause the same basic thing to happen, just at different rates and different frequencies.
Good luck!