36 yr old male w/ pressure in upper abdomen right below the sternum. The ER doc said it could be a peptic ulcer. Taking Prilosec & galviscon. 1 wk later still pressure & feels better lying flat.

See a doctor. It is unclear whether this is gastrointestinal or in some way cardiac related. If your symptoms are persisting they need to be investigated.
Go to see MD. You need to go to see your pmd for eval. You need to get ultrasound of the right upper quadrant of abdomen to see if there is any liver enlargement, and to see if there is any problem with your gallbladder etc. I am concerned perhaps your liver is enlarged that explains the pressure sensation. However, it is impossible to say much without examining you in person. So, go to see your doctor.