these are some of the tips I received last pregnancy from dr. newman to help w/ nipple soreness...
since you are nursing infrequently & w/ pregnancy hormones, your milk supply is typically not plentiful & will change to colostrum-part of the soreness is due to this-to help try massage or warm compresses before nursing to help w/letdown
i found that one side was more sore than the other, so I tried to nurse more on the least sore side
i went back to using lansinoh to help w/ nipple soreness
the first 30 seconds seemed to be the most uncomfortable, so i did try to just "grin & bear it" at the beginning.
my dd was just nursing at bedtime, so i would also have a sippy cup handy and would offer that and snuggling and limit nursing time
since she was very verbal I would ask her to "use a big mouth" and have her open really wide before latching on
i know dr newman has more tips on his website & you can email him directly for more specific help.http://www.bflrc.com/newman/articles.htm
i hope this is helpful. one other thing-if your child is still interested in nursing when the baby comes, don't be surprised if he wants to nurse more frequently when all your milk comes in. my dd was thrilled. it brought my milk in quickly, i had alot, and my ds barely lost any weight, and regained quickly.
best of luck