Sleep Training..help!!

I am posting again about sleep because it's all I can think about these days ..well more like lack of sleep 😢😢. My LO is 4 months and was a horrible sleeper until we purchased the doc-a-tot around 3 months . He slept great in it for about 4 week (5-6 hour stretches). Then almost overnight he started waking every 1-2 hours again.We have bedtime routine,white noise, vibrating contraption and all that good stuff but nothing helps !  I tried transitioning him to his crib in his own room and that was disaster as well. So anyways I purchased this book " the sleep easy solution" and it recommends using a cry it out method for sleep training when baby is 4 months. The book says if you are consistent you can get results in less than a week . I am so torn what to do, not sure if he is too young for this or if CIO is even effective/appropriate method. But I am desperate and willing to try anything, starting to feel so depressed and irritable. Help mamas ! Any recommendations or tips ? Is this normal? Does it get better?