Rubbing alcohol will just dry them out even more. Lips usually chap most in the winter, not the spring. You could be allergic to your mask, you might if allowed try one made of something different. If you're in the military, and I'm no expert here, don't you have health insurance that allows you to see doctors off-base? If it's truly pus, that means you have an infection, and you don't want to let that go on. Now, I'm not sure it is pus, but if it is, again, that means your lips are infected. That isn't necessarily serious, pimples can get infected and exude pus. But I'd want to look into it as soon as possible.