How is his sleep? It's always the very first thing I look into when kids start displaying these types of behaviors.
Has there been anything going around lately? My bunch caught a cold and I've found that they kinda look tired still and just not up to snuff just yet.
Are you spending more time outside because of the nicer weather? Maybe it's tiring him out?
It's weird for this kind of behavior to come up out of the blue but then again, if he really is a mommas boy he may just be entering a stage where he is going to test her love for him.
I once had a major mommas boy only he struggled from day one. He eventually got a little better...until he went on mat leave. We dropped to once per day and it got so bad that I let him go, permanently. I'm not saying that this is what will happen with this DCB though, especially if before he was fine. Hopefully it's just a phase.