In my experience, your issues are common in new AIWB carriers. As @Cory and @Duke have said, it takes a lot of experimentation. It also requires some mental re-training to carry this way comfortably. Keep at it, and you'll get there*.
Now, I vastly prefer it to any other position, and have hiked 100's of miles over rough terrain carrying AIWB.
Here are some things to try:
JM Custom holster. I've tried a lot of other options, and these are by far my favorite.
https://www.jmcustomkydex.com/p/AIWB-WC2-5.html
More flexible belt. I have an Atlas belt and it's way too stiff for AIWB. Try this:
https://www.mastermindtactics.com/shop
The right wedge or cushion. I invented my own "junk carry pillow", and it makes a huge difference.
https://pistol-forum.com/showthread....(AIWB-cushion)
*I have one friend who didn't "get there" with AIWB, even after a lot of trying, and it's because he is a "big boy" around the middle. He now carries OWB at 3:30 and is a happy camper.