we have just had a baby and the first few days the dog was good.but now every time the baby makes a noise or crys the dog barks and will not let me get to the baby,the dog will go for my feet really aggresively.can someone tell me what i can do to stop this

This is too deep and complicated a situation to advice about on the 'net.  Can your vet recommend a registered behaviourist (UKRCB or APBC)?

Definately consult a behaviourist asap. I the meantime i would suggest using a baby gate so that the dog doesn't become a danger to you or your baby. Try to spend as much time as you can with the dog if you do have to keep them seperated so that the dog doesn't feel pushed out.