My turtle is frequently sneezing, coughing, and yawning
It’s okay if your turtle does this occasionally. However, too much could be a sign of a respiratory infection. A common infection is pneumonia.
The recommended thing to do is take your turtle to the veterinarian. They can give your turtle x-rays and antibiotics. Your turtle is going to need a lot of care and chicken soup! (Just kidding on the soup part)
A good prevention technique is to make sure that the temperature in the tank is not too low. Raise the temperature up a little, this will help your turtle’s immune system become more active. Colds, respiratory infections, and pneumonia seem to be the most common cause of death in turtles.
Treatments for this include warmth (for the immune system), antibiotics (oral or injected), steaming, oxygen (water in the lungs means that there isn’t enough oxygen), and x-rays (to check for water in the lungs).