baby sleep. or lack there of

Taryn
My baby boy was born on feb 23. Right from the get go we were super lucky that he seemed to know his days and nights. Night was the only time I would have to wake him to feed. Doctor gave me the ok not to wake him. He would do a 5 hour stretch every night followed by 4 hour stretch. Then up for the day and naps were able 40 min. Not amazing but for the night stretches I'll take it. Those stretches soon combined and from 2 months old until 3 months old he did 9-10 hour stretches. Every night. Without fail. Like clockwork. Then. Out of the blue. It stopped. It has now been 2 weeks of him waking up every two-3 hours at nights. Some nights it's just him waking up and crying but falls back asleep in minutes. Other nights it's screams. Blood curdling screams. I try to not nurse him in fear he will start expecting it. But when he is completely in consolable i nurse and back aslee he goes. Any advice. Has anybody dealt with their baby randomly giving up sleep? I keep hearing sleep regression. Or teething. Either way. What do I do :( how do I get that sleep back :(