Ive noticed that when i lie down in bed at night, i feel like theres kind of a burning feeling in my stomach, almost like heartburn but in my stomach. im also constipated, and theres probably a lot of poop in stomach. what could be causing this?

It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some test. Avoid eating for four hours before going to bed. For constipation - You may take a fiber laxative like Metamucil and drink enough water daily so that your urine is colorless. For the long term you may try to increase your intake of fiber foods.