[Girl Problems] Help me please!?

okay so i started my period in december. i havnt told any of my family , because of the way they treat me. my older sister is always saying stuff like "i cnt wait til you start", and "ugh, still waitin for that day" and stuff like that. so one day i wanted to go swimmin' but i was on my period so i asked my dad to take me to the store so he took me i got some tampons, and they work on me. my sister said that she cant wear them. but i can. so i wore them for 6 days. and i like how you dont feel tha blood come out and stuff. so now im on it. & i need tampons, the pads she has are WAY too big for me. they annoy me! its drivin' me crazy. and i dont want to tell my mom and sister. what should i do?