Oh, I see what's going on now...
My digestive system is pulling shit on me again.
Occasionally, when I take Ritalin, it has no effect until, hours later, it siddenly kicks in.
I've always had a very slow digestive system, and bowel movements are especially infrequent now that I've had gastric bypass surgery and am eating these ridiculously tiny meals.
I can easily go two days without a bowel movement now. It was actually more frequent when I ate more junk, which gave me a loose stomach.