1- Allergic reaction:

exposure to an allergen (a substance, could be passive exposure to tobacco smoke, or something environmental like pollution, or occupational exposure at work or where you live especially if you have changed housing recently. This substance is mainly a protein, that triggers an allergic reaction; your body may have not been allergic to it in the past and this is of new-onset). 

2- Gastro-esophageal Reflux (GER): the stomach content is refluxing back up from the stomach into the esophagus, causing irritation and thus excessive sputum production especially in the morning; you may have associated heartburn, acid taste "acid brash" in the mouth, and sometimes a bitter taste in the posterior part of the tongue. The fact that you have added significant weight makes this very likely.

3- Bronchitis: inflammation of the bronchi (the branches of the trachea into the right and left lungs) which could be a complication of a common cold

4- Post-nasal drip: if your sinuses are engorged with spututm and they're not drained out through the nose, they go back into the throat and you actually feel that you're swallowing sputum.

As you see, the possibilities are quite a few, and it could actually be a combination of the above. You need to check with a chest doctor, maybe get a chest X-ray done to rule out bronchitis, and rule out the presence of any allergies or reflux.