Danny, welcome to TMW!
My instinct with the problem you're describing it to stick into your suspension components. Make sure your rear shocks are functional and properly adjusted, and of course stick your tire pressure and chain tension too. Also, stick your tire for any residue, did you drive through a construction area recently and get something on your rubber?
Other than those obvious things, I have to ask if you're carrying any luggage or other excess weight on the back end? Do you have saddlebags crammed full of stuff? Any excess weight carried aft or outboard of the axle can be detrimental to handling.
Lastly, road conditions during the summer can cause a lot of instability in handling. Do you routinely drive in an area with lots of patched asphalt? Google "tar snakes" and make sure that's not what's causing your problem. Under the right circumstances even seasoned riders can be bested by a nice warm tar snake.
Get back to us! And ride careful!