2 month old coughing

For the last 3 or so weeks my son who will be 3 months this week, has had a pretty nasty sounding cough. I brought him to the doctors a week and a half ago and they said his lungs were clear, his oxygen levels were perfect and they told me he was fine. He still has this cough but no other symptoms, no runny nose, no other symptoms that would make me think it’s just a cold. He’s eating normally, napping normally, and is acting like his normal happy self. I’m not really sure if I should be concerned about the cough or not. He’s not been around anyone who is sick, i stay home with him and he’s not in daycare or exposed to anyone and neither am I. I ’m a first time mom and have no idea what I’m doing 😩