I find that a kisser button has helped my shooting alot. It allows you to have a consistent anchor point which results in good grouping.
You don't NEED a peep sight but most people today will use one.
To sight in a bow you need to have a designated range. I don't think you are using the sight properly once you get it set you leave it you don't adjust it every time you shoot.
For example pace off 20 yards and shoot an arrow. If the arrow is high to where you are aiming move your pin up. Vice versa for if the arrow is low. If the arrow is left move your whole sight left. Once you are shooting consistently by or near the bulls eye you leave your sight. You will then be sighted in at 20.