Re: Very embarrasing question...
I am not expert, but you sound perfectly normal to me.
It's perfectly healthy to become curious about sex at the age you did and to discover you sexuality in the way you have. In my experience most people think about sex frequently and this is nothing to be ashamed about. This is of course how we reproduce and if we did n't think about it we would not do it and would die out as a species! lol. It would be a problem if you were just fuctioning (eating, sleeping ) and thinking of nothing but sex all the time.
Everyone masturbates, everyone has sexual fantasies, this is part of what drives our sexual desire. Don't be upset with yourself for having these thoughts, it is perfectly natural, different people will have different sexual thoughts involving lots of different situations.
Your sex drive will increase around ovulation because this is the time you are more likely to get pregnant so it makes alot of sense to become more intrested in sex at this time, it is hormone related.
I think the fact that you are embarrassed to talk about sex is making you feel you are not "normal" and in you're head you are blowing your "problem" out of all proportion. Hope this helps.