LIBRA GIRL NURSE
you'll need to tell your mum that you have your period, she knows that it's going to happen so she's expecting so really, half the work is done. Just choose a quite private time and say you've got something to tell her. It doesn't need to be a discussion, just letting her know that it's happened, plus you'll need to let her know which Libra products you'll need. It really does take two to fight, so if she is a bit grumpy, you don't need to be grumpy or irritable too - then a fight just can't happen. As to your little sister, ask your mum to not tell her, but she'll find out eventually. Your sister wants a response from you, that's why she teases. The most frustrating thing for your sister would be for you to NOT respond to her teasing, to just smile and walk away, and remind her perhaps that this will be happening to her too one day.
Hopefully your dad is joking about telling people, but just in case you need to let him know how you feel - perhaps talk to his new wife about this, she would be flattered to think that you felt that you could talk to her and it might help the relationship between you.
As to feeling that you are anti social and have low self esteem, these are things that you need to think about dealing with. The anti social tag is because of the low esteem. Why not talk to one of the teachers at school or the councillor - they're there to help, and even if you're not comfortable talking with one of them, they'll be able to find some with whom you do get on. The idea of speaking to a councillor is to find and learn strategies to help you feel that you can cope with life and all that it throws at you, coping mechanisms which you can use for the rest of you life, so I strongly recommend you have a think about giving it a try