Nicky - I'd avoid the Chloroseptic thing. It's designed to numb your throat, which is OK when you're trying to go to sleep. But if you try to sing when your throat is numbed by Chloroseptic, you're likely to do more damage to it because you won't be able to feel the pain. Gargling with warm salt water (1/2 tsp/pint, which approximates the salinity of the body) will strip away any gunk that might be accumulating back there, and will also help to massage the throat a bit.

The first thing to look for in your technique is your breathing. When you're standing with a choir, it's easier to concentrate on getting a good, low breath. When there's a guitar hanging over your stomach, even if you're standing, it's easy not to breathe so deeply because you feel the guitar against your stomach, even when you haven't taken in a big enough breath. Without enough breath, you're trying to use the musculature of the throat and jaw to help get a bigger sound. Hence, vocal fatigue. Find yourself a teacher who'll teach you basic vocal technique, which can apply to ANY style of singing. In the meantime, BREATHE!!!

Good luck.