I really want to keep my baby but dont want to tell mum till later on in life :'(?

ok,i am 16 turning 17 next month. i have a nearly 2 year old baby boy who is such a delight to handle. two weeks ago me and my boyfriend of 2 years found out i was 6 weeks pregnant. i am really scared and i dont know what to do at all. i know everybody i ask for advice just tells me its my own desicision and they are right but i really do need some impartial advice. i live in a foster placement, with foster carers but i am moving out of there in the next two weeks to live in supported lodging. i don't want my mum to know because she has barely got over the fact that i already had a child at 14. i really don't want to hurt my family even though they do not support i feel like there is a chance in the future that things could work out between us but i feel like having another baby will make this family relationship harder to mend since i left home at 13 for personal reasons. my boyfriend is great, he is not even the father of my first child but he is one of the good guys, he is very close to my son and he does everything his real dad can't step up to do. i know he wants to settle down with me and he thinks that his family will be there for me. his family are lovley apart from his sister who i don't get on with.i have been trying very hard to form a relationship with them and now things are finally looking up but i know when they find out, its going to bring me right back to square one. i can't even eat and this worry has triggered not just morning sickness but 'all day' sickness. i am experiencing really harsh mood swings and i seem to take it out on my boyfriend who has been nothing but understanding and there for me, please do not judge my circumstances and try to understand the situation. any good advice will do thanks. also if anybody knows weather i have rights to keep this pregnance from my mum until later on, i know it sounds harsh but its the best thing to do as i havent seen her for a year and a half now. i know i cant keep it from my social worker but does she have to tell my mum or do i have rights to privacy & confidentiality in this case? Thanx in advance.