Absence of fever, how to distinguish pancreas pain from peptic ulcer pain assuming presentation luq burning pain radiating to back?

Cannot without help: Your described symptoms of a burning luq pain can have many possibilities. You have only noted 2 possibilities of many, and likely picked the 2 worst case scenarios. Abdominal pain can have many causes and reasons, and pancreatitis or peptic ulcer would also be associated with severe pain, nausea and vomiting, inability to eat, etc. You yourself cannot tell what you may have; must see a doctor.

RX PUD & AP as one: Source of abdominal pain can be very difficult to identify in the older adult. Due to the vague nature of symptoms that often present with abdominal pain, misdiagnosis is common. A current study showed that the prevalence of PUD in patients with acute pancreatitis was relatively high (52.6%), and the cause may be gastric mucosal ischemia,stressful condition due to AC Pancreatitis. Needs w/u for dx