The real cause is not known yet but it is generally attributed to increased pregnancy hormones. It can be reduced by eating food that is easily digested and not spicy or fatty. It is also advised to split your meals over many small and frequent meals instead of 2 or 3 big meals, not to lie back immediately after a meal and lastly avoid nauseating smells and aromas. Symptoms tend to end by the 16th Week. Consult your doctor for treatment and advise as sometimes vomiting becomes persistent (Hyper emesis gravidarum) and needs hospitalization before deterioration.