My three year old won't listen to me at all

It’s especially bad in public. He will it sit still, he will yell, he will hit. He will throw himself on the ground if he doesn’t get his way and throw horrible tantrums. I feel like I’ve tried everything. I’ve tried gentle parenting, I’ve tried being more disciplinary and assertive and I’m not getting anywhere with him.. is this normal or possible behavior problems? Has anyone been through this and have any advice?