Here goes a long-winded post. Sorry y'all, I just have to talk to people that may understand.
So, DS is 3 months and has been on alimentum for 2 months due to a suspected MPI. He also has severe reflux and is on a combination of zantac and prevacid per the pedi (I hate giving him meds). I went in for a check up on Monday because he was having more spit up, not sleeping, and very cranky. He has only gained 8 oz in a little over a month. The pedi wanted me to switch him to similac for spit up to see if it would help his spit up, so he could gain weight. She doesn't think he has a MPI, but the other pedi in the practice, who used to be my pedi, does. Since putting him on the similac he has been screaming, has a low fever, arching his back, and just passed a stool with black in it. I called the pedi and she said to keep him on the formula and to give him gripe water for gas/upset stomach. Also, to watch him and his BM's in case this persists and I will bring him in.
If this were you, would you put your baby back on the alimentum because he tolerated it even though he spit up more? I hate seeing him in pain and I don't know what the right decision is. It is such a heartbreaking situation, IMO. I don't want it to get any worse and I don't think I can take another day of non-stop screaming.

Re: MPI (milk protein intolerance)