[MacGuffin]

I will let you in on something you may or may not know: parents are usually a lot smarter than we give them credit. Assuming they love you and pay attention to you, eight times out of ten they just know these kinds of things. So there is a chance your mom already might suspect that this kind of thing is going on. It wouldn't be surprising, anyway.

Regardless, this is a choice that is entirely up to you. If you feel the need to talk to your mom about it, then talk to her about it. Be honest with her. However, if you are going to do that, I suggest that you do it because you want to do it, not just because you feel guilty and therefore obligated to tell her such a thing. There is no reason to logically feel guilty for being a teen and experimenting safely and responsibly, which it sounds like you are doing. Your first responsibility is to yourself and your own health and well-being, not to your mother.