WORRIED ABOUT THE SHOT

I read online that it can stop your periods forever. I'm 15. I don't want kids now but I do want kids when I'm in my 20s but if the shot stops periods forever, doesn't that mean I can't get pregnant? There's no egg to fertilise because of no periods. 
My boyfriend keeps wording every time we have unprotected sex that I am pregnant but there's a 1 in 100 chance that i could be pregnant and it worries me slightly.