Achalasia. This is a disease where the nerves of the esophagus no longer function to coordinate the muscles to push down food, or send a signal to the lower valve of the esophagus at the entrance to the stomach to open an let the food in. Cause usually unknown. Most effective and most invasive treatment is surgically cutting the muscle of the valve, that can be done laparoscopically or endoscopically (poem).
Specialist . You need to see a gastroenterologist for treatment and follow up on these conditions. .
All the time. There are many causes of dysphagia. If you have achalasia, the best treatment is an esophageal myotomy.