It may b bcz of acidity.  reduce spicy nd fried foods. Drink lot of fluids

It's nothing but indigestion and there is no short cuts, you can follow what Anchal and shipra said.

it could be indigestion. you might have eaten fried or spicy food which is difficult to digest in pregnancy. so due to acidity,  it might come back in your mouth. dnt lau down after eating food and keep urself hydrated during pregnancy. consult your doctor regarding this.

Have small frequent meals. Walk for 10 min after each meal. Avoid spicy and fried foods and take lots of lots of liquids especially water.