Access concentration is actually more of a gentle effort thing... kind of like how much presence it takes to shuffle a pack of cards. Enough control that the cards don't go flying everywhere, enough effort to bend and snap the cards, but enough looseness and lack of rigid control that allows the cards have the room and ability to snap out of your hands, and enough sensitivity to feel the sensations and adjust the energy of the the shuffle. Imagine you are gently shuffling an endless deck of cards - that's a good mental image, except the deck of cards here is the meditation object (awareness of the texture and sensation of breathing).
Sounds like you are "concentrating" too hard. The word concentration is unfortunately used to mean "really trying hard at something", but the real intention of getting concentrated is becoming more and more "centered" around the meditation object. Being centered is about balance, a gentle kind of adjustment of effort.
So actually your early stages of sitting are probably access concentration. Try sitting and putting your attention on the breathing sensations... and simply do that. Try using less and less effort while still gently holding the breath in awareness. That's it. If you actually stay with that, gently returning to the attention of breathing if your mind wanders, you will naturally develop a light jhana and go through all of the nanas, through Stream Entry and beyond.
It's actually very simple, people over complicated it. So don't over complicate it!