A burning, acidic feeling in the mid to lower chest is oftentimes experienced during pregnancy due to slower digestion and regurgitation of stomach acids. This can be exacerbated when lying down.
Sitting upright and “over the head” stretching exercises may provide relief. Mild antacids used in small quantities may also provide relief (Tums, Rolaids, and liquid antacids such as Mylanta and Maalox).
If these mild antacids don’t help, you may try over-the-counter Pepcid AC, Tagamet, or Zantac. Avoid Alka Seltzer.