Aches are pretty normal in the early stages of learning to play.

Try doing this exercise using 5, 8, 6, 8, 7, 8 for a few days, the 4, 7, 5, 7 etc. for a few days, then start on 3, and keep working from there.

Don't overdo it. Pinkies take some time to train.

The 'random misbehaving finger problem' for me is a middle finger that wants to stick up when not being used, so I end up looking like I'm flipping the bird to anyone looking in my direction (seriously risky when busking)