How can I become more comfortable with affection?

No matter what the relationship I have with someone, whether it’s emotional or physical, I struggle with showing or accepting affection. Deep down, that’s all I want to do but when a moment like that arises, I freeze. Trying to hug me is like hugging a wall, trying to compliment or comfort me is like talking to an iceberg. Either I’m really awkward or very distant but I don’t want to be. I don’t know why I do this. It is extremely frustrating, I’m basically a deer in the headlights when someone is trying to show me affection, even if I love them a lot. What can I do to change?