Re: Probable bowel blockage, what should be my course of action?

It could possibly be a (slightly) irritated colon - that can give the symptoms you describe. I speak from long experience unfortunately.
What happens if you take laxatives? If the constipation gets worse this might indicate irritation.
Regardless, I would suggest you stop eating/drinking anything that might be an irritant. In my case ordinary black tea had a really negative effect - I used to drink bucket loads of the stuff - at one point it got so bad I went under 9 stone, at 6'2". It could be imagined that coffee/coke/spicy foods etc would also have a bad effect.
I would not get overly worried about producing fine log-shaped fæces. I think that the 'log' itself is rectally produced by the compression of the many small pieces that emerge from the intestine.
There are no doubt many other possibilities - I don't know much about parasites, but there seem to be many here who think they can cause a multitude of intestinal problems. I vaguely remember also reading on here that in certain circumstances the neural or muscle transmitters can be irreparably damaged, causing more or less permanent constipation.
Dehydration or magnesium deficiency are other factors that can cause it.
In any case, good luck with finding the cause.