What color is the mucus?
With kittens, anytime you are in doubt is the time to seek a vet. However, I am also of the opinion that many times, vets will prescribe antibiotics when they are not indicated. And, while there are those who will disagree with me, if the color of the mucus is clear or yellow, so long as it is watery and thin, antibiotics are not indicated. Antibiotics will only address a problem that is in fact bacterial in nature. Thin, watery, clear or yellow mucus indicates a VIRAL load, not bacterial. Bacterial infections are normally seen with thick, pus-like, yellowish-green mucus and can ~only~ be treated with an antibiotic. Both viruses and bacterial infections can bring on a fever, so that isn't always an indication either. Viral issues must be allowed to run their course. Sometimes, a virus can evolve into a bacterial problem, and yes, then antibiotics would be indicated. But to give an antibiotic when one isn't indicated only serves *IMO* to weaken a developing immune system in a young kitten.
Talk candidly with your vet and remember to ask intelligent, educated questions. If you are going to take this kitten in to be seen then ask if it is a viral problem or is it a bacterial problem. If your vet tells you it is viral, then it may not be the best course of action to medicate with antibiotics at this time.
Best of luck,