It's probably because of the general attitude in the environment where you grew up. My parents' generation were totally ashamed of anything to do with sex and mostly pretended the subject didn't exist. We attended a conservative church that railed against pornography so much they seemed obsessed with the subject. And I went to a liberal high school where the sex education topics made me blush too.

Do you remember how embarassed everyone was during sex education lessons in elementary or middle school? That's the shame we learned from our parents and people who still retain the belief that talking openly about sex is taboo. And the funny things is that when my church had sermons on the sex/porn taboo, adults got the same flushed embarassed attitude as sixth graders in a sex education class and couldn't look each other in the eye.

And I think it's rubbish when writers and magazines say everyone masturbates. No one can prove such a 100% statement. Your feelings are actually on the spectrum of what counts as normal today. And even if you aren't religious, a lot of our social norms come from various religions. Even people I know in non-western countries have basically adopted Christian restrictions about sex, homosexuality, etc. Most of us (including my Buddhist relatives) live like Christians who don't attend church.

I tend to have a more clinical view of things because I think about life as biology. If some people like sex and some don't, it's fine with me so long as laws aren't being broken and no one is being forced or harmed. There is no right or wrong in a biological function.

The big issue is whether sex or a specific activity goes against your own moral or religious beliefs. That's when people struggle with conscience and some turn to undesirable behaviors to deal with their feelings of guilt or desires they feel are embarassing.

If the activities you engage in or wish to engage in violate your idea of right or wrong, maybe you could think about why you think it might be wrong and whether you have basis for that belief. For example, if you feel as if a God might be watching your and keeping score about all the times you had sex, try to think of why God would care if one person had sex or mastubated.

Forgive me if I'm rather blunt, but my opinion is that if you're not harming anyone it's nobody's business. I'm actually afraid to speak my mind around my more conservative friends, so I totally understand how you might feel embarasssed about the topic. You seem perfectly normal to me and if others express views that certain acts are shameful or dirty, just realize that people operate on different belief systems and accept that you don't need to convince others to agree with you on what's normal and you don't have to conform to their idea of what you should and shouldn't do in private.