Thanks for the post!
Generally hiccups stop after some time. In your case since they have been troubling you for more than two years, you should look at other causes of Phrenic nerve irritation like metabolic disturbances as in diabetes, smoking, alcohol intake and acidosis of kidney origin or uremia. Tumors or neighboring substances pressing on the nerve too can hiccups. A wrong sensation of something in the esophagus too behaves similarly and can be seen in GERD or reflux disease. Anxiety and stress to trigger this and so also brain tumors or infections.
This needs a detailed investigation. I think you should discuss this with your doctor. You may need to undergo blood tests to rule out diabetes, acidosis etc. and CT scans to rule outtumors. It is difficult to comment beyond this at this stage. Please let me know if there is any thing else and do keep me posted. Take care!
Please read this article, may help..