Child Have Congested Cough And Ear Infection. Can These Problem Can Cause Him To Be Nauseous?

Hi there. My son is 2 1/2 yrs old; weighs 33lbs. He has had a "congested" cough since we can remember with only 1 diagnosed ear infection (last week). He is usually a healthy, happy, active toddler; however, about once a month, we notice a day when he seems off...a tad pale or "green". He looks as if he may vomit, but doesn't. This happens a few times in between bouts of running around and enjoying life. Maybe this is just another crazy toddler behavior we won't understand about our child, but thought I'd throw it out there...could his baseline congestion cause him to be nauseous?