How do I get my dog to stop doing this?

It's really annoying. Any time I carry her somewhere, she'll crawl and scratch at me. Sometimes she even sticks her paws down my shirt and it really hurts. :( Why is she like this? She even does this when I'm just sitting with her too, at times. Why? I tell her no firmly, but she keeps doing it. My mom doesn't know what to do, either. She does this to her, too.