Sleep regression from hell

Li

My LO has always been a good sleeper. We put him down drowsy at 7, wake up once around 4, then go right back to sleep until 7. For the past week it takes a while to get him down, and then he wakes up every couple hours crying and will cry for a long time until I give in and give him the boob and/or let him in our bed. We’re exhausted and not sure what to do. Any advice?