I'm in your boat, more or less. I'm 32.5 weeks pregnant and have been nursing my toddler all throughout the pregnancy with varying degrees of pain, ranging from agony to mild irritation. Right now I'm at the mild irritation point. When it was agony, I had some real problems. I tried to explain it to him but he didn't understand and started saying some negative things about wishing I didn't have a baby in my tummy that was making my "mumnums" hurt when he drank milk. Then I decided to just deal with it - and practice my relaxation techniques while he nursed in preparation for relaxing during childbirth!
He too is pretty relentless - no substituting daddy's cuddling for nursing to sleep or anything like that. I kept thinking that at some point my milk would taste bad to him or that I'd stop producing it and that would be the end of it. That hasn't happened yet, so we'll see.
I wonder also about how his nursing will affect the timing of the birth - will it cause me to go into labor earlier?
Anyway, it's just a matter of time - either they'll stop or we'll give birth - either way it should be less painful at some point in the near future, right?!