And should l be alarmed and take my teenage son to see his doctor? My husband said that his side will bother him if he runs.

tell him to drink lots of water when he runs.
water will keep him hydrated, therefor he will not be cramping in his sides while running. this happens to alot of people but they dont realize there dehydrated

yes, its normal. just tell him to breathe in through his nose and out through his mouth

Well does he have asthma or any other illness if so before he runs make him try using his inhaler 30 minutes prior to running. If he does not have asthma and it hurts l think your best choice would to be bringing him to a doctor. Something that little can turn into something serious always remember that