Almost 3 years old. slight cough, fever. no wheezing, small mucus, fast breathing, active. not feeding well but drinking water and peeing. worried?

Worried, but ok: It sounds most likely to be a respiratory virus. This should hit it's peak around 3-5 days, with cough and congestion going away after 10-14 days. Watch for fever over 102.5, poor urine output, lethargy, irritability, breathing over 40/min, difficulty breathing with stomach and neck muscle use, or wheezing. If those develop, bring him in.

See MD: Is child on meds now? Is child obese? Needs to be properly seen by MD. Chest x-ray? Pulse oxygen level? Please see pediatrician and put mind at ease!