Have you tried Boots own brand lipsalve? It's a stick type and comes in a number of flavours, I use the spearmint one. I find it much better than branded ones, it's very moisturising and doesn't leave that nasty white residue round your lips that some do, I really hate that.
That's why I use it ;)
I just remembered, I had a lot of dry lip trouble last winter and bought a tiny tube of Blistex intensive moisturiser, really worked well. Didn't need to use it for long and still have most of this little tube left. Might be worth a go for particularly troublesome times.
I like Carmex too but when I've had really bad dry and chapped/cracked lips (especially when I have a cold) Blistex cream is the only one that has helped, fantastic stuff and agree with the others who recommended it.
I have Sjogrens/Sicca Syndrome too so have a very dry mouth and lips generally.