I thought i inhaled a piece of food 4 days ago now i have a cough but no wheezing. could it just be post nasal drip or could food be in my lungs?

Possible: It is possible that there is some food particle in your lung and this may lead to pneumonia. If you have had a cough prior to aspiration of food, it is possible that your current cough is from post-nasal drips. However if you still have problem beyond a week or if the cough gets worse, best to consult your doctor who may order a chest x-ray.

Irritated cough refl: Josh, A much more likely scenario is you irritated the tissues that trigger a cough reflex (designed to protect your lungs). After an episode like this they may be more sensitive than normal for a week or two.