Your symptoms seem consistent with gastroesophageal reflux disease as your doctor has suggested.
Exercise aggravates reflux.
Ranitine is a good acid blocker but there are much more potent drugs available that are needed in patients who do not respond well to ranitidine alone, for example Prilosec, Prevacid, Aciphex etc. Sometimes a combination of these more potent drugs aka PPI's is used along with a dose of night time ranitidine.