Since I woke up my cat has been sneezing constantly and very frequently. Is it a cold, and what medicine should I give?

Sneezing can be a sign of respiratory infection or merely a physiological reaction, so it does not always mean illness. With accompanying nasal discharge the cat is likely sick and a cat cold medicine helps; recurring or feverish cases warrant a vet visit and, if needed, a fever-reducing medication after a clear diagnosis.