Sleep problems

My baby boy will be 4 months on Monday. He had been sleeping 7 hours through the night 2-3 weeks ago, and suddenly he stopped. He’s in the sleep sack not being swaddled as he rolls to his stomach periodically. He now wakes after 1-2 hours and scream cries until we bring him to bed with us and I nurse him back to sleep. He was fine in the bassinet before but now he won’t stay in it. I need help figuring out what is causing his awful sleep habits. I’m seriously going crazy 😭