Hello and Thank You for using Just Answer. The behaviors of your son are all completely within the normal range for a two year old who now has to deal with a new sibling in his life. Before, he was the king who got all of the attention. Since he cannot verbally explain his jealousy of the new baby, he has tantrums, bangs his head, and will not eat all for attention and to manifset that he is still in control of some things. Take a deep breath, relax, and be patient. You are not a bad parent and your son is not a bad child. It is a natural part of his development.
For his behavior, start praising the times when he behaves well and make a REALLY big deal about it. Keep a sticker chart of characters that he likes and give him a sticker for each day that he behaves. You can also give him a sticker for days he behaves at school and then at home as well. After 5 stickers, and they do not have to be on consecutive days, give him a little special treat or a special outing. Then after a few weeks, change the number to 10. You are trying to focus more on the positive behavior to eliminate the negative. When he misbehaves, just remind him of the rules and give him a time out and leave the issue alone. His bad behavior does not warrant so much attention.
As for his eating, for now just keep offering healthy foods and get him to eat whatever you can but not junk food. If the eating issue becomes a serious concern, please contact his pediatrician. Many parents supplement their children's diets with Pediasure so that they are getting some required nutrients.
Hope this helps.
Have a great day!!!