This happens to me all the time. Here is my take on it.
If you are flying in a mountainous area and you are skimming the top of the mountains, ATC is going to do its best to keep you atleast 1000-2000 feet above the ground. So you might find yourself going up and down. When you are on approach there is nothing you can do but ride it out. You can try to make gradual climbs and decents to keep from having too much up and down motion. I know it is anoying, that is why my pax have sick bags in the seat pockets.
As far as the back and forth freq. switching, I think that is due to being on the border of two airspaces. That is the only thing I can attribute that to. If possible I try to not tune over the most recent requency. I will tune in the hand off freq. in com 2 so if they make me go back to the original freq. I can switch to com 1. Not all radios can do this, but if you have one that allows you to use both com 1 and 2 it is kind of handy. Plus it is nice to be able to dial in the ATIS on com 2 before you make your approach, then switch back to com 1 to talk to ATC.
