mucus in stool, heart burn, and pain in the upper left under my breast, goes away for a little while after eating yogurt.
Your upper GI symptoms are most likely related to acid reflux. Dairy often helps with soothing the irritation of the esophagus which is why you may be finding some relief with yogurt. Chronic cases (GERD) need to be investigated as there could be a host of causes either or the LES (lower esophageal sphincter) or surrounding structures that may contributing to it. Gastritis and a peptic ulcer may also be responsible, which would also respond to dairy.
However it is also important to exclude cardiac (heart) conditions. Although this would not respond to dairy, it could nevertheless be present and being missed. Depending on your age, medical history and current health status, your doctor may consider various tests as outlined in the following article :
It is important to ascertain whether there is actual mucus in the stool or whether you are experiencing a fats in the stool (steatorrhea). Often the two conditions are confused. You don’t mention other lower GI symptoms so the mucus may be unrelated to the upper GI symptoms.
Part of the colon does lie under the rib cage so it is possible that your all your symptoms could be related to the lower gut, with conditions like inflammatory bowel disease. You can find a list of causes of mucus in your stool in this article – http://www.healthhype.com/what-causes-mucus-in-bowel-movement.html
You should see your doctor who will consider doing further tests like an endoscopy, stool test and even a colonoscopy. Other investigations may also be considered. This will help with a proper diagnosis and treatment.