I just PM'd you, but thought I would also post this here, in case someone else has something similar and is looking for answers.
I'm not sure if this is what your chick has, but I had two little chicks get "vent gleet", which is kind of like thrush or a yeast infection in its digestive system. They had white, smelly stuff that would constantly run down out of their vents and stick to their body - it was so acidic that it removed the feathers in that area (I was washing one of them and didn't realize I had a tiny cut on my finger until it stung).
My chicks were also about 2 weeks old when I discovered it -- one at 13 days old and then one more a couple days later. The second chick (my only LB) had been pecked a lot and was bloody when I found it - I think the stress contributed to it getting the 'vent gleet'. The first chick was never pecked on.
I did separate them from the other chicks. At first, I only had one chick with this and I put it in with a healthy chick (as a buddy) and even after being together a few days, the healthy one never caught it. After I found another chick with this problem, I removed the healthy one and put the two sick ones together.
I mixed together:
* plain yogurt (1/8 tsp per chick) plain is better than vanilla or flavored because it has less sugar - also make sure there are other live cultures in it beside just the acidophilus
* extra acidophilus (broke open capsules and pored a tiny bit into the yogurt)
* 1 drop polyvisol 'without' iron per chick (baby vitamins)
I then gave each chick 2 droppers worth (droppers were not full) once or twice a day (aimed for twice, but forgot sometimes). Whenever there was a healthy chick in the infirmery with them (from being pecked on), I would also give the healthy chick one dropperful, as a preventative measure.
They are now 4 1/2 weeks old. My light brahma chick is all better (was better in less than 2 weeks) - the easter egger took a little longer - it looks like it may have just finished healing (it was the first one to get sick and took almost 3 weeks to get over this). None of the other 23 chicks ever came down with it.