If it's frequent, then maybe it's your diete, stress levels, or some other aspect of lifestyle. Peptobismol, Gaviscon, or similar thick indigestion liquid should help. Rennies or similar tablets can neutralise some acid, but don't really stop overproduction of acid. If it's causing you a lot of problems, try something with ranitidine in it (I forget the names, but they look like little tablets). Failing that, go to the Dr, and he/she's prob give you Omeprazole or Lansoprazole which are pretty superb drugs.