I see a white residue in the back of my throat. I think it's just a piece of food, but it always gets stuck there! What can I do?

Needs a look! White stuff in the throat may represent a fungal infection called thrush which is easily treated with medication. Difficulty swallowing may be a reflection of this or another serious problem. I would want a physician such as an ENT to take a look at this.
See ent. This could be chronic irritation or sign of something much more serious. See throat specialist.