What Should I Do About Persistent Stuffy Nose After Initial Side Effects Ever Since Starting On Janumet For Diabetes?

Hello, my dad (66 years old) is diagnosed with diabetes. His doctor prescribed him Janumet 50/1000 3 times a day (half tablet in the morning and afternoon, 1 tablet in the evening). He experienced some side effects like fatigue, vertigo, stuffy nose. etc in the first week. Fatigue and vertigo somehow stopped after the first week but he is still struggling with a stuffy nose now, it especially strengthens in the evenings and at night. His doctor advised him to use nasal sprays and he is using one now. I would like to ask your advice on this case.