this is due to regurgitation of stomach content. in pregnancy
most of the abdominal space is filled by growing uterus
in which fetus is growing. by this intra abdominal pressure is increased so content of stomach is regurgitating.
to prevent this eat in small quantity but more regularly like every 2-3 hourly. eat lite food containing less oil or ghee, easily digestible food. when u sleep ur head end of ur bed is raised aroud 10-20 degree. before sleeping eat less & intermittently u can eat little things like biscuits etc. take some milk intermittently.