Nausea can be a symptom of so many things. Have you had regular chest x-rays of your lungs?
Welcome to the forum!
Nausea can be the symptom of many things. The commonest cause being GERD and acidity. This is also possible with medications. Constipation, gall bladder problems, IBS etc can all cause nausea.
Please discuss this with your doctor. Please let me know if there is any thing else and do keep me posted. Take care!