glad you've been reassured! I was the same too. Those first couple of sucks KILLED, but then it subsided. Mine lasted til about 6ish weeks, too, then one day it just stopped. - Like having a really bad ulcer, then one day you wake up and it's gone!
Just keep in mind, although BF is natural, our poor nipples aren't used to being sucked on so often and they need some time to toughen up