Unable to sleep well at night

My baby is 4months old, when he was about 8weeks old he could differentiate I guess between morning and night because at night he can sleep for 4hrs straight, here I was happy that I can now sleep well at night and suddenly boom! I can't even get an hour of sleep cos he keeps rolling on his bed and I have to breastfeed to make him sleep back, we keep doing this till morning, am confused of the sudden change please I need advice thanks!