Help!! My chocolate lab goes insaine when he sees other dogs!?

I have a 1 and a half year old chocolate lab and when we go on walks and we come across another dog i make him sit but he whines and he lunges at full speed at the dog and pulls me along with him. There are many times when i have walked him in the rain and we saw a dog and i was on the gr and he pulled me right to the dog! Now whenever i see the girl that has that dog she turns the other way cuz i cant hold my dog! Just today i was walking him on a path and a guy with a poodle walked by and he whinned and whinned and he tried to lunge for it and whn i saw him on the way back he turned around and walked the other way avoiding me!!!! It sooooo imbrarsing! I have the prong collar and still no result.My mom wont even think about going on a walk with him! Im the one who always walks him! And he has also ran out of the backyard to go and see another dog, he just takes off full speed!! I need help quick!! I can't keep having him do this!!!