Testing can be helpful and certainly isn't harmful other than the process of getting blood drawn (which is obviously harder in a 20 month old).

Allergies can make reflux worse. If there is a food sensitivity it can irritate the entire GI system. When this happens GI meds may help but often not as much as you would expect. My 14 year old niece was having chronic stomach problems. 30 mg of Prevacid just wasn't helping anymore. She went off of dairy and feels much better. Now though we're wondering if it's the dairy or simply that many of the greasy foods she prefers have dairy and she's now avoiding them. I made her dairy free cupcakes and her stomach ache was back.....

My other niece is allergic to peanuts and her blood testing showed very low sensitivity to egg, dairy and wheat. She was able to continue to consume these without any issues but does have to avoid peanuts.

Best of Luck - Stephanie