Friend, I am sorry Stormy is sneezing more often than usual. In response to your question, sneezing can be caused by many different medical conditions. It will be difficult for me to determine the exact underlying cause without a hands-on examination. But, common causes are allergies, a cold, dust/smoke, a foreign body in the nasal cavity, nasal polyps, etc. to name a few causes.
I am going to make some recommendations that you can try if he continues to sneeze the next step would be a hands-on examination with your family veterinarian. This is what you can try:
1- Open the hot water in your bathroom and allow him to breathe the steam/vapor for 5 minutes 2-3 times a day.
2- Benadryl (diphenhydramine) 25mg tablet every 12 hours for 3-5 days. You can buy Benadryl over the counter in any pharmacy.
3- If no improvement after doing the above I would have him checked by your family veterinarian for a hands-on examination.
My goal is to provide you with excellent service - I hope I've provided the information you were seeking, if you feel you have received anything less, please reply back as I am happy to address follow-up questions. Kindly rate me when you are done.