It's your "personal choice" not to use birth control, but you have made the "personal choice" to flood your body with massive doses of hormones much more often than recommended? How is that different than the things you disagree with about birth control? What did you think was in Plan B?
In your shoes, I'd look into getting an IUD. It's natural in its function and not hormone-based. I don't know that Plan B would cause sterility, but would be worried it might cause cancer. That's a lot of hormones.
Plan B is meant to be used only in emergency situations and should try to be avoided as much as possible, as it is a very large dose of hormones all at once. I don't think it would cause you to become sterile, as there are no studies or anything that say that will happen, but I am not totally sure as the information on Plan B is limited because of it being a fairly new 'medication'. Though if you don't want to become pregnant, you really need to be using some other form of birth control in addition to condoms, because condoms are less effective against preventing pregnancy than most female birth control methods. You are already taking lots of hormones with all of the Plan B pills you have taken, so it's not as if you are avoiding taking hormones. If you don't like having to remember to take a birth control pill every day, then look into having the depo shot, vaginal ring, implant, etc. all of which you don't have to do daily. You really want to avoid taking Plan B anymore, as it is not healthy to keep taking.