Welcome back to JustAnswer.
Many things can cause nausea. But related to your history of diabetes, how are your blood sugar readings lately? Hyperglycemia (eleveated blood sugar) can cause nausea, as well as other symptoms like fatigue, thirst, frequent urination, itching skin, and dry mouth.
There are several GI (gastrointestinal) problems, such as gastroparesis (slowed stomach), acid stomach or ulcer, gall bladder issues (especially if noted after a meal containingt fatty food), gastric reflux, intestinal infection, etc.with nausea as a symptom.
Sometimes nausea occurs along with inner ear problems, but usually there would also be balance problems or dizziness if this was the cause.
There are many more things that can cause nausea.
Are you having any other symptoms?