It's totally normal. I have, myself, experienced this in past relationships. Some men are attracted to butts, some breasts, and etc. It sounds like your husband finds your behind attractive and cute and sexy and since he is the only one who sees it naked, this is a show of affectionate, loving intimacy for him. I agree with the others--it is important that, if you're uncomfortable with this, to ask him to stop and that he honor that request. Otherwise, I absolutely encourage you to tell him that you are unfamiliar with certain displays of intimacy, and explain why: you did a great job of explaining to us, and you can do the same with your husband. It is so important to have that communication--intimacy is not only about sex, it is also about your emotional connection and communication. And, since you are newlyweds, it is important to begin now! Also, if you are communicating openly you will feel more comfortable trying new things...maybe. I'm not saying you have to, I'm just saying you never know.

I'm so glad you felt comfortable to ask your question here. I hope you feel comfortable coming back.