Baby wakes up 4 to 5 times in middle of night !!!! Help!

My baby will turn 6mos and its been almost 2 weeks that he wakes up very often in the middle of the night crying, a loud cry ! I breast feed him, he sleeps and i put him down on his crib and 20 -45 mins later he's up again crying !! And it continues to happen..ive also put him in bed with me and still wakes up crying, even if he's asleep in my arms ! And i he sometimes stays awake til almost 4am :( Anybodies babies going throught this ? Could it be teething? But i mean its only at nights when this happens ! Pleasee help