Causes of persistent nausea include gastroparesis, chemotherapy, motion sickness, stomach flu and food poisoning, according to Mayo Clinic. Individuals with gastroparesis have problems digesting their food, because their stomach wall muscles do not function correctly. Nausea can occur with or without vomiting.
Heart attacks, middle ear infections, high fever in children and traumatic brain injury can cause persistent nausea, notes Mayo Clinic. Pregnant women may experience nausea, which they can ease by taking ginger tea, peppermint candy, or inhaling lemon or peppermint essential oils, notes Everyday Health. Ginger is also effective in calming chemotherapy-related nausea. Peppermint relaxes the stomach muscles, which aids digestion. However, individuals with gastroesophageal reflux disease and nausea should avoid peppermint.