I also use to feel really guilty for masturbating (I'm a Christian and also have a degree in Biblical Studies). I've come to the conclusion that it isn't really wrong in and of itself, like someone above said babies and children do it too. I personally think I started doing it around 5. Had NO clue what I was doing. It just felt good and honestly I more used it for practicality's sake. Long road trips, pressing down there felt good, gave alternative feelings, and kept me from having to pee for longer periods of time. I think when masturbation is used to sin that it becomes a sin. If you are doing it and it makes you lust after others and commit adultery in your mind then it is wrong. If you are using it to ignore problems you are facing and making yourself feel better so you avoid seeking God's help, I think it is wrong. Also, if it causes you to not share this area/act with your husband than I believe it is wrong. All in all I think masturbation is often an appropriate and acceptable thing to do. If you are still worried about these emotional feelings and lust and the fact that your mind so easily wanders to this I strongly encourage you to read, "Every Woman's Battle" by Ethridge. It's a very good Christian book that can help show you where lines need to be drawn and helps people deal with the emotional aspects of these issues.

Try not to be too hard on yourself though, we are all human and fall short of the glory of God. All we can do is try to obey and better ourselves.