I think what you are describing is pilot induced oscillations, have a look at this video
eA0jZXck2S4
While helicopters are dynamically unstable in the hover, you shouldn't be moving the controls constantly. Try establishing a stable hover - then if you keep the controls steady, it shouldn't go anywhere, but this will only last for a few seconds before correction is needed. Things get easier the less you move them.
I'm almost done with my helicopter PPL, the first thing my instructor always mentions after lifting is "stop moving the cyclic!!" I don't even realise I'm doing it..