Sleep Training

Little guy is 4 months old. He slept like a CHAMP the last couple months. I’m talking 8pm-7am. I did the taking cara babies newborn sleep course and it really worked wonders. The 3/4 month class is not working for my boy at all. Between the four month sleep regression, and his routine being all out of whack from him just getting over a sickness, I don’t know what to do. What success have any of you mommas had when it comes to sleep training/sleep programs? any tips? because this is insanely hard 😭