Weaning advice? (somewhat long)

MaritimeMama3

Hi ladies! I've never intro'd, so I'll quickly tell you I'm a mom to a rambunctious 18 month old, who I've been nursing the entire time, and who seems to prefer breast milk to solid food. 

I'm once again pregnant, and I'm anemic. I'm also underweight (I didn't start out that way, but slowly kept losing weight while nursing LO). I'm weak and tired and have constant headaches. I need to wean, full stop. We're down to nursing once before bed, once in the middle of the night, and once in the morning. He usually nurses to sleep. Last night, I let him nurse for half an hour, then handed him to DH. He screamed for an HOUR. DH went in to comfort him, but he just would not fall asleep. Finally at 10:45pm, I caved and let him nurse to sleep. If he wakes in the middle of the night and DH goes in, he'll just cry and cry. I'm sure I've caused this by reinforcing the habit, but I need it to stop now. 

I feel SO incredibly guilty! To make matters worse, his growth is slowing down (he's down 20 percentile points in weight, and 10 in height) and is becoming anemic. Ugh. This is awful.

Thanks in advance for any help/advice you can offer.