T.H.
My son usually has a cough that goes along with his allergies. It sounds kinda bad, but it really is only related to allergies. Their sinuses drain and trickle down the back of their throat causing some irritation, so they cough. We have found that Zyrtec (we use the generic) has worked the best for my little guy. He is also 2.5. His issues can last a few days to a few weeks. It is hard to know what is going on, but unless other symptoms pop up we usually chalk it up to allergies.