Sleep routine Help!

My 3 month is having a lot of trouble sleeping or staying a sleep! We usually start the bedtime

Routine around 8-9pm, he gets feed , a book and Rocked to sleep but once I think he is out cold and I put him down he freaks so I pick him up for rocking then he is sleeping and put down but an hour later is crying !! I don’t know what to do ... he won’t fall asleep till like 11/12 then wake up for feeding around 2am and won’t go back to bed till 3/4am... I start work in 2 weeks and need help !!!!