I am sorry for your loss also. FWIW, children have long been weaned during pregancy in traditional societies, for thousands, if not millions of years. Birth spacings are typically 4 years apart (although 3-5 yrs is common), mother regains fertility for a short time, gets pregnant, the nursing child weans a few months into pregnancy. The pattern goes on for about twenty years, a woman has 4-5 children. The last child likely nurses the longest. I digress, but my point was that nursing into pregancy is common for humans and how the species evolved. The primary difference though is that child and mother slept together, so mother was not sleep deprived. Western sleeping arrangments, with mother and child separated make it very hard on the nursing relationship, and exhausting!
My thoughts are with you. I would look further into your OB's reccomendation though per weaning. Hugs to you, it seems you are going through a very rough time.