Hugo and I scoured the Internet for clues from other parents, discovering in the meantime that there is a plethora of frightening information available for susceptible parents! No surprise there. Fortunately Hugo came across a post from a mother who said that her lactation consultant told her the blood and mucus were caused by an excess of lactose in the milk, due to the baby getting mostly foremilk and missing out on the hindmilk. (Foremilk is sweeter --thus more lactose which is milk sugar --- and more watery to satisfy thirst, and hindmilk, which comes after, is creamier and richer to satisfy hunger.)
The solution to this problem is to lie on your back while nursing so that the milk has a better chance of mixing in the breast. I switched immediately to lying-down nursing (not the most convenient thing to do though I must say it is relaxing) and by the next morning Weston's poop was completely normal again. About a week later I also realized that he had stopped grunting or groaning when he had to poop!
At this point I am doing a mix of back-lying, side-lying, and sitting-up feeding, but I have noticed that he is happiest, most relaxed, and most satisfied when I nurse him while lying on my back. He loves being able to fall asleep on me like this.
Of course Oliver wants to join in the cuddling (not the nursing) on occasion which leads to situations like this:
