9 month old sleep….HELP ME!!!!!

Please help. I am so tired and losing my mind. Baby just turned 9 months old. Since he started crawling and standing this past month he has regressed but never been a great sleeper to begin with. I think his longest stretch of sleep ever was 4 hours maybe a couple of times. I am so tired and cosleeping but trying to get him to sleep in his own room for the whole night. Everynight I get him down in his own room in crib. He puts himself to sleep most of the time but wakes up after 30-45 mins, then we start the process all over for him to again wake up 30-45 minutes later. I am just so lost on how to sleep train a baby that wakes up 5-12+ times a night. He wakes up SCREAMING. I try not to intervene but he just screams and screams and doesn’t calm down. I am so sleep deprived and struggling. Please help me I am not sure what to do.

For bedtime we put him down between 7-7:30 depending on how well he napped that day/when he last woke up. We do bath, lotion diaper jamie’s, feed, read 2 books, sleep sack, sound machine, lights off. He always falls asleep so quick and easy but after first wake up everything goes downhill and he seems very agitated and just wants to be held.

Baby wakes up because he has startle reflex and moves once then just keep moving till he cries. I am willing to look into sleep specialist I am just nervous it won’t work. Any advice welcome!