My 2.8 yrold has runny nose- and a cough at night-- no fever-- 2 days in.. he's had tons of colds -this time his nasal discharge is thicker and yellow?

Sounds like : Postnasal drainage causing the coughing spells . Need antihistamine to take care of the colds which eventually takes care of the cough. Change in color of colds does not indicate bacterial infection , virus ,allergies can do the same. Watchful waiting and supportive treatment at this time since he is not running fever. See Peds if condition worsened.