I am going to give you a suggestion on treating Frankie for the gas. Simethicone/ GasX is often used to relieve intestinal gas pain. If you scroll down on this page you will see a listing for the GasX and can follow the dosing instructions which for a small dog would be 1/4 of an adult dose. http://www.walkervalleyvet.com/otc-meds.htm
The next thing I would do is to have a fecal sent out for analysis to be sure that you are not dealing with a hidden parasite like Giardia that can cause serious gas pain in the intestinal tract.
Dogs can develop food intollerance at times even if they have been on the same food for a long period of time The most common causes of food intollerance in dogs are beef, dairy products, chicken, lamb, fish, eggs, corn, wheat, and soy.
The following article discusses how to do a food trial in-depth . It is recommended to try a different protein source such as duck, rabbit, kangroo or Bison and grain free We often see dogs do well on a different protein only to develop an problem to this as well later down the road.
This is for a food trial:
When trying a food trail it is very important that they get no other foods no treats or human foods as this will void out the food trial. This can take 6-8 weeks to show improvement so you must stick with it.
The last thing I would try is a Probiotic to help the gut flora in the intestinal tract. Forte Flora made by Purina which may help with the problems you are seeing. Joan