What can I do if my 4 month old baby have sleep regression and how long does it last?

Oh the 4 month sleep regression is so real, I remember going through this with my girl and it really tested my patience! What helped us was trying to keep a consistent bedtime routine, like a short bath, feed, then some gentle rocking before putting her down. It does pass lah, hang in there, most mums I know said it lasted around 2 to 6 weeks for their little ones. You are doing great for even noticing the pattern, first time mum instincts are spot on.