Why is my baby's head so DAMN ITCHY!!!

Guys.... This is a mystery. My 4 month old keeps itching at the back of his head!!! He will try to reach back there and scratch scratch scratch until he is red and raw! He will also turn his head side to side when laying down. His pediatrician was so concerned that she sent us to the hospital for seizures. We stayed there for THREE DAYS AND WE STILL CAN'T FIGURE OUT WHY HE IS DOING THAT. Its is not seizures thank god! We went to an ear doctor, ears r fine, neuro, brain is normal, cardio, heart is strong. We finally saw a gastro and had a poop test which came back with blood. So he is allergic to soy and dairy, which i removed completely from my diet (EBF) i even got rid of all my freezer stash and started over 😭Its been 6wks and no more blood in stool. But he is still itchy! I had my lice lady who comes and checks my girls every so often to check him and all is clear! Nothing else is itchy, no rash, i am at a loss. Idk what to do to help him. I put lavender oil, hydrocortisone, aveeno baths but its persistent.

ANY IDEAS WHAT IT COULD BE???