Hi, if I were in your situation I would be making an appointment with the citizens advice bureaux (C.A.B.) and they will take you under their wing to sort out finacial help and housing of some sort. Your mum will be getting child benefit for you no doubt, is she passing this onto you?
It doesnt sound like you can rely on your family too much. My hubby and sis were also chucked out at 16 due to the step father so I wouldnt rely on your mum now - time to grow up for real and stand on your own feet it sounds like, and think of yours and your babies future.
How long can you stay with your nana? The last thing you nee is to be worrying about having a roof over yourt head and you'll need to be able to have some where permanent when the baby arrives.
You'll be entitled now to a £3 voucher a week to buy fruit and veg and milk, so get that sorted with the c.a.b. or go to the job seekers place for that.
Try not to worry too much, in 10 years time you'll look back at this ime and hopeflly see how strong a person you are to get through this time.
ps Just a few more things, you should be entitled to a £500 grant 11 weks before youre due that doesnt have to be paid back, and if you get set up with some accomodaton go to the Salvation Army and they should help you with kitting out with furniture.
I would start thinking practicle now as time goes really quickly!