I think it's possible, if you're coughing a lot or just had an attack. The asthma itself shouldn't be causing a stomach ache, though, because asthma is in the lungs.
Is it possible that you have allergies that could cause the stomachaches? My little sister has asthma, GERD, a casien allergy, and a whey allergy. Her allergist told us it's really common for someone with asthma to have other allergeries and things like that.
Hope this helps!
It's possible that muscle soreness in the stomach could occur from coughing vigorously...it's also possible to develop anxiety related stomach issues from it...but I don't think that asthma itself can cause a stomachache.
Some asthma medications could cause upset stomach...the pills, not inhalers.
My third oldest son used to complain about stomachaches all the time when he was younger...and he's had asthma since birth. But I think it was mainly because he didn't want to go to school...that's where most of his attacks happened. We had to change schools because the one he had been attending was built into the side of a hill...lots of places for the mold to hide...and that's what set off his attacks.
Hope that helped.