Hello and hope you are doing well.
The burning sensation could be due to heartburn. To reduce acid levels try good life style measures. Take frequent small meals. Avoid spicy and oily food. Eat dinner about two hours before sleeping. Elevate the head end of the bed. Keep a food diary and note down what aggravates your symptoms and avoid them. Ensure to maintain optimum weight by regular exercise. Avoid NSAID's, quit smoking, eliminate alcohol, avoid caffeinated beverages and reduce stress levels. OTC antacids can further aid in reducing acid levels. These measures need to be practiced long term for results. Please consult your primary care physician for proper assessment.
Hope this helped and do keep us posted.
You should probably make an appointment to discuss this with your doctor, but it's most likely not dangerous. The flip flop is probably just common PVCs which are harmless unless you have heart disease. twice in one day is normal, there are many that have tens of thousands a day and even that is not dangerous. A PVC is simply when the lower chamber of your heart beats too soon causing that flip flop feeling. You should get the pain in your chest checked out to be safe.
Jon