abdominal pain and rash

My son is 8 he has had abdominal pain in the lower left quadrant and around the belly button on and off for about a month. The pain will wake him at night and he cannot move because of the pain. First thoughts i had were his appendix. The pain is not severe all the time but when he gets it he cannot move, pain goes down the legs. By morning, he is fine!
Just recently, he started to develop a rash on his hands and feet, sometimes on the stomach that come and go. The rash is red and extremely itchy. It also only lasts a short period. He has seen an allergy specialist and no real allegies are present or noted by the specialist. He has asthma and takes medicine each night. Asthma seems to be controlled. Should I be worried about these two symptoms being related? 1st symptom diagnosed as constipation, second one as something he ate. Not sure what to do?

[TJ72]

My son is 5 1/2 and has been diagnosed with asthma for about a 1 1/2  years.  He has been tested for allergies 3 times, 1 said yes and 2 no as far as allergies.  However, during a good portion of the year he suffers from stomach pains that have him crying, sleepless, cranky and just not feeling well.  He has had ultrasounds, GI Barium Test done and they just tell me he has a sensitive stomach.  I have a friend who also has a daughter with Asthma who is having the same stomach issues and the doctors can't tell her anything either.  Did you find out anything on your sone?