I get a lot of hartburn and don't know why?

Usually gerd: Signs and symptoms of gerd include acid reflux and heartburn. The basic cause of heartburn is lower esophageal sphincter that doesn't tighten as it should. Two major causes are too much food in the stomach (overeating) or too much pressure on the stomach (frequently from obesity or pregnancy). Certain foods commonly relax the les, including tomatoes, citrus fruit including tomatoes, garlic, onions.