Simon and Ben, thank you both.
Ben, I don't get infections after every ride by any means, though I understand your point about contact with other riders and non-combatants. It seems to be the same infection, which recurs every few weeks, though antibiotics shift it if I take them. I'm wondering if maybe I need a slightly longer course to get rid of it completely, though I know chronic sinusitis is pretty common. It may be a complete coincidence that I've picked this up since I started cycling so much but I suspect not and I suspect I need to be a bit more careful about spacing my rides out, especially the longer ones and, as Vorsprung implied, keep it ticking over in between.
Simon, that is some serious riding you quoted there, even for a youngster! I can well believe it took a long time to get back to normal. Can you remember, though, whether or not you were more susceptible to colds and stuff like that during that time?
Thanks again, both.