Welcome to the forum. Your boy is a cutie Btw, looking at his pic, his smaller head size looks like my boy's head condition as well ... the top part is narrower than the rest.
Seb has sub-clinical seizures which are detected from his EEGs. He's on epilim to keep them under control, along with diazepam for stablising effect for his seizures and hypertonia. Your description of your boy's constant fussing, crying, jumpiness and needing to be carried all the time matches exactly how Seb was like during his 1st 6 months. The only time he wasn't fussing etc was when he was sleeping and he was such a light sleeper. He was on phenobarbitol then ... it made him irritable and cranky. He was such a cross baby all the time! Phenobarb couldn't keep all the seizures under control so when he was 3 months, his doc put him on epilim instead, which was much much better for him.