Hi K.,
My son is now 8 1/2 months old and I had the same issue with him right around the 3 month old mark. I'm happy to report that I'm still breastfeeding and he's doing great. Hopefully my experience can help you.
First, the green poop. My son's poop was yellow and seedy (normal for breastfed babies) for a long time, then it started to turn green. I was told by my pediatrician that as babies get older and begin to nurse less often (no longer every 2 hours), their poop gets darker and begins to turn greenish. I believe it has something to do with the milk being in their digestive system longer.
Second, the mucous and blood in the poop. For my son, it was a definite allergic reaction to cow's milk in my diet. I immediately eliminated all dairy - milk, cheese, yogurt, ice cream, etc. My pediatrician told me I could still eat eggs, but I decided to cut back on that, too. Prior to eliminating the dairy, my son was EXTREMELY gassy and I was giving him gas drops at every feeding. He was also really fussy at times. Once I stopped consuming the dairy, I noticed that he was less gassy and the the mucousy poop stopped. He also stopped having blood in his stool as well. I was told that it can take 2-3 weeks for dairy to get out of your system. I don't know if that's true, but I think I noticed a complete change in my son's poop (and fussiness) around the two week mark.
Eliminating dairy was kind of challenging for me because I'm a non-meat eater and that was a good source of my protien. So, I still consume a lot of soy (which has no adverse affects on my son), beans, whole grains, and nuts. I also eat a lot of veggies and salads, but I found the best way to do that in the beginning was to eat smaller portions, for example, rather than a really big salad. Certain veggies can produce more gas than others, i.e., broccoli and cabbage. You may just need to experiment with the veggies to see which ones you can eat in smaller amounts.
I think there are many factors that can contribute to a mother's "milk drying up." But, from my experience and research, it's very important to drink TONS of water during the day. Also, our breasts produce milk when they are empty, so the more you nurse (and the longer your baby stays on the breast), the more milk you're likely to produce. It could be that your husband's coworker stopped nursing as frequently or there was some other change that caused her milk supply to lessen.
Two very good resources I highly recommend are www.breastfeeding.com and Le Leche League (you can find them online as well).
Most importantly, though, is to go with your motherly instincts. If you feel something is still not right with your son, definitely keep getting him checked out.
I hope this helps!