I think it always takes some time for Nexium to work because the acid has caused a burn on this delicate tissue, and it takes a while for it to heal. In your case it has progressed all the way to an ulcer, so I don't think it's surprising if it takes months for this to heal.
You could get tested for Celiac disease. If you are allergic to gluten, only stopping gluten will stop GERD symptoms for you.
If you've been on the nexium and you've changed your diet to a GERD-friendly one and the symptoms continue, have you been scoped yet? If not, it's time to ask your doc for more testing. Ask to be tested for H. pylori and have an upper endoscopy done to get an idea of what your esophagus, stomach and duodenum look like.
All PPIs have side-effects that can be more serious than weight gain. So verify you've got GERD and find out what else you can do to keep the situation under control.
SYLIVA I HAVE ACID REFLUX I TAKE PRILOSEC 20 MGS NEXIUM COMES IN TABLES EVERYMORING YES THEY COULD CAUSE WEIGHT GAIN.