Asthma in 3 month old

So about a month ago, my son had RSV. He recovered within 2 weeks and has been perfectly fine since then.

Tonight I noticed his chest was slightly sucking in like it was when he was sick. He's not wheezing, nostrils aren't flaring, he's eating normally and nothing has turned blue. I even counted his breaths per minute and that's normal.

I'm trying to figure out why he may be slightly struggling to breathe. I don't think he's at the point in which we need another ER visit and I will call his doctor in the morning.

I'm just wondering if anyone here had a baby that had rsv and then they developed asthma after that.