I don't know if you have to have hemmroids in order to have "pencil poo", but it seems a lot of IBSers have it. Even my poo gets narrower when my guts are acting up. Probably because it's not in there long enough to get properly bulked up.
Anyways, about your morning porridge. Actually, that can set you off even if just a few minutes after eating it. That website for the IBS diet that got posted a day or two ago mentions this. As soon as you eat something, it sends a message through your entire digestive tract, "Get ready, something's coming." For people who's guts don't work properly, that message to be prepared is translated as, "OMG, here it is! Now, now, NOW!" and so just eating something can trigger your intestines to spasam and release whatever half-formed stool they are holding in there, even though your porridge hasn't even hit your stomach yet. Sometimes anything you eat can do this--regardless of what it is--whereas sometimes it's something specific that does wait to get to your stomach and then it fires everything up based on its conent (e.g. high fat triggers the gall bladder when it gets to the stomach, which, in turn, can trigger the intestines to release at that moment).