My symptoms: bumps on back of tongue (not tastebuds), clogged nostrils (decongestants don't work), bad breath. Took cephalex. Symptoms remain. Please hel?

Allergy? You may have an allergy to something. I would not take any antibiotics until you see a doctor for an evaluation. You can try an antihistamine like claratin, zyrtek, or Benadryl (diphenhydramine) to see if you congestion improves. If not then you may be suffering from a viral infection and that should resolve on its own in a couple of weeks. If symptoms persist, see a doctor.
Sore throat treatmen. There are 2 diagnoses that can explain your symptoms. The first is a sore throat, pharyngitis, which can be caused my many different types of organisms. Unfortunately, most of these organisms will not be killed by the cephalexin. You need to be evaluated for a different antibiotic, possibly with a throat culture. The second possibility is esophagitis, which can be caused by high stomach acid.