potty regression

my son has been potty trained since 1.5 completely trained since 2 (not peeing at night). we welcomed a baby brother 2 months ago and thats when the problems started. at first he would pee the bed maybe once a week but since then he has gradually progressed to almost every day. i got him pull ups for the night but he cries and tells me diapers are for babies and hes not a baby. how can i get him to stop peeing the bed as i am tired of washing sheets every day. We go potty right b4 bed and stop drinking lots of liquids about 30 mins b4 bed. he pees at random times. he wakes up and goes to my room asking for clothes because "someone wet him" i once told him it was pee and he started crying wondering why someone would pee on him.