Just because you can't hear any wheezing doesn't mean that it isn't happening inside the lungs. It isn't always audible, and sometimes can only be heard with a stethoscope and some kids with asthma don't wheeze at all, they may crackle or bubble inside the lungs.
I would set up an appt with a pulmonologist or allergy specialist for a more thorough exam. Because asthma can be so serious and an attack can happen at any time I would get seen by a specialist if you have concerns.
Katie, mom to Olivia (97), Veda (98), Franky (2004), Wendy (2005), JoHannah (2007), Thea (2009) and Sunny (2011)