Help!

So im about to be 17 in 3 months and me and my boyfriend thinks that im pregnant but i don't know when is the right time to tell my mom. I'm scared of what she's going to tell me and if she's going to make me tell my dad. My sister says that the symptoms im having are signs of pregnancy but im scared to find out. I'm still trying to figure out how im going to tell him because i feel he's going to leave me.