I can appreciate your reluctance to talk about sex. My background was kind of like that too and sex education was lacking for me as a teenager. Well being naive ended up with me getting pregnant.

I think depending on safe and not safe days as a method of birth control is risky and could backfire. You might consider getting a couple of condoms and keeping them in your purse. Then the next time you are about to have sex, hand him one and tell him to put it on. (or you can put it on him yourself). Otherwise you might actually need to buy those diapers mentioned above

It is easy to say there is nothing to be ashamed of when talking about sex, but in some cultures it is still sort of a taboo subject. Really though it is a natural human function and no worse than talking about eating or sleeping. You really don't have to be ashamed and really need to talk about this if you are going to have sex with a guy. The consequences of not having that conversation are much to severe. It is ok for you to bring up the subject, If you wait for him it may not happen