help me get my 4 month old to sleep

J

his sleep regression ended two weeks ago. then we had 1.5 normal weeks of sleep. last 2 nights he has become a new child. i rock him and he flails his arms around. i couldnt get him to settle no matter what i did. i tried laying him.down and hed wake right up and cry. after 6 hours i couldnt get him to sleep even while holding and rocking him. i am.loosing my sanity please help