Hi Alex.
I was 19 with my 1st baby. On No 4 now at the age of 37, so that should tell you its not all bad!!
Its YOUR body and YOUR baby, sounds like you have a good BF and his family for support you. If you familt no now sooner than later it will give them time to get over it. But I'm sure you Mum will be with you every step of the way, after all its her Grandchild.
Hope it all goes well, I'm on due March thread so if you fancy a chat........
Jo x x x