Sleep Regression

Help!! My 2.5yr old boy has always slept through the night from 6 weeks (lucky I know!!) He recently moved into a single bed and within 2 weeks he was waking up nearly 5 times a night. He had an iron deficiency which we’ve dealt with, but he is still waking constantly and coming to get me and gets upset when he can’t get back to sleep. We don’t know what to do to help him sleep through again. Ironically my baby (6 months) has been sleeping through since he started waking! Help!