My 2 year old doesn't feel pain

Hi there, My name is Stephanie. I am the mom to a two year old little boy. Just a little back story, then I'll get to the concerns I have. I'm hoping someone can help me. My son is biologically not mine. He is my husband's son and we recently went through a termination of parental rights of the biological mother and a step parent adoption. My husband made a terrible decision while intoxicated and it led to him getting the girl pregnant. He was unaware of the pregnancy until after she gave birth. At which point she contacted my (then) boyfriend to tell him that she just had a baby and it was his. She gave birth two months early. Anyways, she has a history of drug abuse. Admitted to using methamphetamine for the first three months of her pregnancy. She smoked the entire duration of the pregnancy and occasionally drank. (No wonder he came two months early, I would have wanted out of there too!) It took a lot of time and resources to locate her and the baby for a paternity test. It was confirmed that he was indeed my husband's son. Once that was confirmed, he initiated a custody agreement. She never complied until one day she dropped him off with us and we never saw her again. We didn't get him full time from her until he was 15 months old. He didn't walk. Didn't talk. Only weighed 14 pounds. He would shove mounds of food in his mouth and would so much he would throw up. Anyways long story short, she is no longer a part of his life. He is now two and a half years old. He is currently in our state's Early Childhood Intervention program because of cognitive delays. When he was evaluated, he was 17 months old and was placed on the level of a 9 month old. He is now making great strides to getting caught up. We work with him daily. He has developed a secure bond to me and you can tell he is a happy toddler. However, we are starting to have some great concerns. We've discussed it all with his pediatrician and he has been referred to a specialist at the children's hospital but we are on a waiting list. I wanted to reach out here and get the opinions of real people who might be going through the same thing. First, he doesn't feel pain. Just a few days ago, he jumped face first off the couch and almost bit through his lip. There was blood everywhere and he just looked me and got mad that he had blood on his hands. But never cried out in pain. I think I cried more than he did. He is so clumsy and bumps his head all the time. Never even a whimper. He does cry, don't mistake that. He cries when he is hungry or mad. But never out of pain. He has a 'daredevil' tendencies that scare the hell out of me. We have stairs in our home and I will not let him go down them after he literally tried flying down them one time. I don't trust him to go down them without trying to fly. He started to develop these little skin tag looking things. He was diagnosed with molluscum contagiosum. He will sit there and pull them off without a wince. Secondly, he self harms. He will bite himself. At one point, we had to shave his head because he would rip out clumps of hair out of anger. He will bang his head on the wall. I know tantrums are normal 2 year old behavior, but is this normal? It's been happening since we got him at 15 months. It has gotten better but he still does it more often that I feel is normal. He has the temper of a grown man and sometimes I feel like he has unusual strength. Lastly, he is motivated by food. It's no secret to us that he went without food before we got him full time. However, we've had him over a year now and he still acts like he is starving. He will eat food out of the trash and off the floor - at home and at daycare. He gets three meals a day plus two snacks. We do not give sugar or juice. He drinks water and whole milk and he gets two Pedisure shakes a day. We have gotten him to gain about 10 pounds in the past year but he is still very low on the percentile chart (less than 3%). He will not gain weight no matter how much he eats. He doesn't have the ability to stop. He will eat and ask for more and more and if given, he will throw up. We are waiting on an appointment with GI specialist but I don't know if the problem is with his GI or if it's mental. I worry about him and his health. I am desperate. I do not have children of my own. Just him. And at this point, I feel like I am doing something wrong or failing him. I know his life is now significantly better than it was but it doesn't stop me from feeling like I'm failing him. He has had to literally fight for his life since the day he was born. He's experienced more in his two and a half years than most of us experience in a lifetime. Any help or advice would greatly be appreciated. Maybe someone else out there has experienced this with a child born to a drug addicted mother that used during pregnancy. Does it get easier? Will he grow out of it? Thank you, Stephanie