I know several mentioned lifting your baby higher with a pillow or other solutions, but if you are like me, you just love looking at your baby and so naturally your head tilts down therefore your shoulders draw in... it's a natural position that your body gets into for that purpose and yes, very painful for your shoulders, neck and back.
Massages are great way to help start the healing process but does get pricey. Try going every other week until it's fixed. It will get fixed if you have a good massage therapist. Also, if you found a good one, he/she will be able to demonstrate stretches for maintenance purposes so it doesn't happen again. You do need to get it worked out though because most likely your shoulders and neck muscles are already "triggered" to that position and even changing your posture will not help once your muscles are in that state.
BTW - I am a licensed massage therapist and a mother of two and I went through the same thing with my first. With my second I knew to be more careful about allowing my muscles to become "triggered" from breastfeeding. Good luck and grats!