How should I tell my SO?

My so and I have been together for about 3 weeks now so we’re still figuring our dynamic out. However, she’s very touchy. I’m not. I’m in pain a lot of the time due to health issues and thus I don’t like being touched. The majority of the time being touched, even if it’s something as simple as holding hands, causes my body to have an adverse reaction. On top of that, I’m asexual. I’m not interested in sex really at all, her and I have had a sexual moment and I didn’t like it. I don’t regret it and it was consensual, it just made me realize that I’m not ready for sex or that sex is something that I don’t want. I know she wants a sexual relationship with our romantic relationship, and I don’t want to let her down. I don’t want to tell her to stop showing me affection cause I don’t want her to feel bad or that I don’t want to be seen with her. It just feels like we’re moving too fast. Every time she’s tried to kiss me recently I move my head or turn the attention to something. I don’t know what to do. I like her a lot, I just don’t like the pda and physical affection. I don’t know how to tell her.