Marsha, I know you do purely BLW, but it might be an idea to give him some high fibre cereal in the morning mixed with water.
for example, All Bran cereal, softened in water and you feed it to him. This way he gets water and fibre in and with you feeding him, he would get a bit more then when he does it himself.
Just and idea, feel free to ignore obviously, but constipation usually clears up with more fluids and more fibre.
Also you can add some probiotics to his diet, this will help the green poop, which is sometimes a bacteria, it will enhance the good bacteria,which will help with any inflammation and with constipation.
HTH!