Concerning behavior and movements in my 10 month old

A few months ago my son began having trembling, shaking movements in his arms and upper body. We had an EEG done and ruled out any seizure activity. I now believe they are intention tremors, as they occur mainly when he's focused on holding small objects, for example picking up a cheerio and putting it in his mouth. To add to this  last week he started holding his arms up and flexing/twisting his left wrist in a strange manner. He does this many times p/day. Along with this came a type of eye twitch like an exaggerated blink while frowning. He flaps his arms about a lot, when excited or upset, or sometimes just when he's sitting there. He also startles extremely easily and is noise sensitive.
He does seem alert and has learned to wave, clap and say a couple of words, but his gross motor skills are delayed. He's nowhere near crawling, has only rolled over a hand full of times, and still can't push up well in tummy time, instead he just screams. To me, it appears he has weakness in his arms. I should mention I could be to blame for this because of lack of tummy time when he was younger (he had GERD and would spit up terribly when on his belly). With all that said I don't know if the gross motor skill delay has any connection with the other symptoms.
Any thoughts greatly appreciated. Thank you.