It depends on what the "big blob of poop" was. I mean that if this big (how big?) poop is also abnormal in shape and, if you break it, you see that it contains ingested hair, it could be difficult to pass, blocking, thus, the poop following it. Gas can adversely affect the intestinal flora, so the mushy poops indicate exactly this: an inbalanced situation in your bunny's guts.
Keep on the hay, don't give any veggies until the mushy poops (they are not cecotrops, right?? Cecotrops are just like a grape bunch, are extremely soft, green, smelly and, sometimes, jelly-like) stop appearing. Are they mushy or diarrhea-like?
Is he now eating a lot of hay? Does he continue to have an appetite?
Marietta