I'm still thinking thyroid, although I know that the ppi's can cause weight gain in some people.
I was on levothyroxine for many years and really couldn't tell any difference in the way I felt... always tired, slowly gaining weight that wouldn't come off, despite exercising 2 hours/day. Finally, I was so sick of being pudgy that I had cosmetic surgery to get my old self back. I sold a truck to pay for that one. Still, the weight slowly came back until I weighed more than before the surgery! Then, one day when I had the flu and was very stressed at work, I began to have heart issues that made me feel like I was going to die. Five cardiologists later, I had a cardiac ablation that was supposed to fix everything. Well, I woke up from it with the same issue as before going into the hospital. Fast forward a few years...
I finally put two and two together to equal THYROID! Then I started reading and found the website I gave you. Many people, I would venture around 60% to 70% of those who take levothyroxine (Synthroid, thyroxine, synthetic T4, whatever you want to call it), do not get real benefits from it. Also, most doctors only dose by the TSH test, a worthless gauge of your pituitary gland, not your thyroid (mine is always near 0, medication or none, telling the docs that I am hyperthyroid, not hypothyroid). When I finally found a doctor who takes many things into consideration (Free T4, Free T3, diet, weight, energy level, etc.) and switched me to natural desiccated thyroid and T3 (liothyronine, Cytomel), I began to feel like a new person. I have lots of energy and can get things done. I can barely feel my weird heart beat and I don't have angina anymore. My weight became normal for my frame at 120 lbs., though since the gerd I am only back up to 112.
So I take it you are still on the Nexium/ppi's after six years? Have you ever tried natural ways to get off of them? That would be my first suggestion, to get off of the ppi's. This is how I did it: www.healingwell.com/community/default.aspx?f=45&m=3144102&g=3144817#m3144817
I hope you're eating very small meals (like a couple of tablespoonfuls at a time). With the hiatal hernia, the bigger you eat, the worse it will be.
I still say get adequate thyroid testing, get your results, and educate yourself about
them. Read the website (all of it). Find a doctor who will do something different.