Hi, Lisa. I felt the same way when I started. Some things that helped me:
Premo, not Kato. Not sure what you're using now, but if it's Kato, I would set it aside until you're more experienced. It's very hard to sand to a high finish.
Make sure you've baked long enough and and the higher end of the correct range for the brand.
It doesn't take that long. A few moments with each grit is fine - just enough to rough up the entire surface. Going over and over it accomplishes nothing but sore fingers. What works for me is a mixture of types - considered taboo, but I do it anyway. Black wet and dry sandpaper at 400 grit, then 3M sponges in fine, ultrafine, microfine, then - if I want a high polish - 1500, 2000, 2500 wet and dry sandpaper. I only spend moments at each grit and I spray down the piece and the sandpaper each time (I use a spray bottle instead of a bowl of water).
Remember that you're scratching the surface - your goal is to make the scratches smaller each time until they are gone as far as your eye is concerned. To do that, you want to be sure to remove the grit from the previous round before you start on the next one. That's why some people do it under running water and I spritz it. Everyone rinses somehow.
I hand buff with a cloth diaper. If I have round beads, I put them on a skewer and put that in the dremel and run it inside the diaper. If I want a high shine, I always buff with the dremel. The buffing may be your problem, not the sanding. If you use a dremel, you need to touch it so lightly that if you put it against your hand while it's running it just tickles. I started with a string wheel because it was easier not damage the piece. Now I use a muslin wheel and turn the battery dremel up to 6 (electric to 4) and the shine comes up much faster. If you turn the dremel it too high you build up too much heat and damage the surface. If you're using a buffing wheel, think about it in the same terms.
Since I don't spend much time on sanding - maybe 30 seconds per grit - I don't resent it if I get to buff level and discover an area I should have done better - do-over isn't such a big deal.
Hope that helps some. It's one of those things that eventually comes together and gets easier for you, but seems like it never will.