Using Older Sister’s Birth Control?

So my sister recently has gotten off birth control bc now she wants to have a baby so she had three leftover packs that she didn’t mind giving me. I have never used birth control bf my mom won’t let me get on it for some reason but sister thinks it’s ok. I just want to see if it’s ok to use my sister’s birth control? It hasnt expired yet and won’t for a while. My boyfriend comes back in town next month and we haven’t seen each other since Christmas break since he is a college and i’m still in high school and we want to have a special night when he gets back. And hopefully i’ll be fully protected from pregnancy by then. Please don’t leave any rude comments i’m new to this birth control thing lol just give me help/suggestions