Hi, I just saw this, sorry. I wanted to say that my son was exactly like this until about 3/4 months old.
We had to go on Neocate also, which made things worse for us, BUT we went on Elecare (which is the same thing as Neocate, just a different company) and it got better. However, every poop on Elecare was runny, but he felt a lot better.
The black streaks are a sign of blood. You really need to get things checked out.
Also, I know my son had anal stenosis. Bascially his anus was really really tight. He could not get the poop out, if he did it was very runny, because the runny stuff got by the hard stuff.
He0 struggled with getting gas out on his own. After many trips to the GI doctor and in the hospital, Finally they concluded this.
All I had to do was anal stretches 2 times a day. I had to put vaselline on my pinky finger with a glove and insert it half way and wiggle side to side, to stretch his anus.
Everytime I did this, he let out HUGE amounts of gas and poop.
After about a month, he was fine.
He is now on Nutramigen and everything is going great.
I would just mention this to your doctor.
Hugs to you, Wendy