A little self-conscious during sex

Au
Before I explain, my boyfriend doesn't judge me at all. But, I still feel self-conscious during sexual stuff. Like, I want to do 69 with him, but I'm just so shy about my back side. And he wants to have sex doggy style, but again, I'm still so shy. He reassures me he can wait for kinky stuff like that, and that he doesn't judge me at all. I don't know why I'm so shy with my back side. Any help with how I can get over this? I want to experiment with him, but I'm having trouble breaking out of my shell. Any help please?