he fights his sleep

Every single freaking time!! It doesn't matter if I catch it early enough he will not go to sleep until he has screamed kicked and cried his eyes out :( 4 months and he just keeps fighting his sleep. How do you guys do it? I'll catch him when he starts yawning or looking tired and try to put him to sleep but it just doesn't work for him. I'm tired of him always having to cry his eyes out before he can finally sleep I feel like a failure for not being able to rock him to sleep. I'll carry him sing quietly do everything but it just doesn't work