I have been taking 20 mg of prilosec and 300mg of zantac (ranitidine) for 3 months. the acid is still not under control should i double the prilosec?

See your doctor!: There might be reasons why the medications aren't working. First of all, it may not just be excess acid. Depending on your age and other risks, ulcers and cancer (esophageal or stomach) might need to be ruled out by an endoscopy test, abdominal ultrasound, or other tests. Also, reflux issues might require changes in diet and weight, less alcohol, smoking, Aspirin -advil-type drugs, etc.

Acid reflux: Have you modified your diet to (temporarily) eliminate food triggers like acidic foods (tomatoes, lemons, limes, oj, soda pop), caffeine, fried/fatty foods, spicy foods, onions? Is your weight under control? Do you take any meds that might trigger acid reflux: beta blockers, erythromycins, tetracyclines, etc? Have you had an upper gi/endoscopy to check for abnormalities? See doc b4 changing doses.