I have had ups and downs with this myself and with the kids, but when it gets to be more often than not they or I are screaming, snapping, etc.,...I've had to take a look at other factors.

I just recently found out that some allergy meds can cause folks to be grouchy or worse (like shouldn't they print that really BIG on the bottle??).
Prob. some other meds might have similar effects...and these can take a while to build up.
I do have severe enough allergies to be completely laid-out in bed if I don't take something some times during the year...so I've had to get with an allergy specialist, adjust and change meds when they don't fit. Am also taking allergy shots to deal with the underlying allergy. Hope to be on allergy meds only another year or two.

I am MUCH happier now on a diff. allergy med, as is my son. He's also had crankiness/edginess with albuterol for his asthma. If your child is on anything at all, it might be worth it to check out whether of not this is a factor taking things up a notch.