Cos ours seems random and ad hoc.
Both my DCs are possibly mildly asthmatic. Neither have been beyond the GP giving both, separately, months apart, a blue Ventolin inhaler to ease some low-grade wheeziness. Neither have been to a specialist but to be clear, I don't think either of them need to see a specialist!
Both DCs, 13 and 15, occasionally use Ventolin for this wheeziness, by which I mean, one maybe one dose a week, the other one dose every 2nd or 3rd day (he's a hay-fever sufferer as well). This seems to help with the bit of tightness they get. They have no other health problems.
When they run out (I confess they share the inhaler!), I have to write a note to the GP's practice, drop it in, wait 4 or 5 hours, go back in, pick up the script and get it filled. I ask for 2 as one is supposed to stay in school with matron.
Is this how you manage yours under similar circumstances?