Puppy wont walk on a leash, what can I do/?

My 13 week old mastiff pup wont walk on a leash. She walks behind me and if I pulled her I'd be dragging her which I am not going to do. I did training cles with another dog I had and recall the trainer told me to use a head collar for walking problems, I tried that but then she just sits down and bats at her head. She only does half way well when I have my other dog along, but that is not always possible. It seems she is very fearfull, not of people but of cars, a ball bouncing, loud noises,ect. Well I dont want to use a choker because I dont want to hurt her neck, how can I get her to walk with me without pulling her?