Usually i can rock 4 month baby to sleep, but now he is very fussy, won't take the pacifier and only falls asleep on my nipple? why? and what to do?!

Possible teething: At that age, it's possible he is starting to teeth, and is using your nipple to soothe his aching gums. You don't want to get into a routine of him using you to soothe himself at bedtime - it's a difficult habit to break. Try massaging his gums, use a cool teething ring, or try a dose of ibuprofen if he;s really fussy. Likely this will pass with the eruption of some teeth!!

Stop: You have an opportunity every day to teach your baby to be an independent sleeper. First you only rock when fully awake, so you both can enjoy the togetherness. Once he is drowsy he should be put down to fall asleep alone.You have essentially never delivered the baby, you have taught him to need you continuously.Sit nearby if you need to, but put him down and teach him he can get to sleep alone.