Sensitive Stomach

[Woodnymph]

Dog foods with Grains,additives,chemicals cause skin,stomach problems. Try Taste Of The Wild,Bison or others like it.... Google it and you will see. I used to cook for my dogs, which ended the stomach-skin issues. After 2007, people woke up and demanded food without cheap grains. I have been feeding my dogs this food for 3,1/2 yrs. NO problems. Don't just believe the "Natural" claims, but get familiar with what's really in these dog foods.

[Freedom]

You can learn about dog foods and how to read labels here:
www.dogfoodanalysis.com

For a start, read a few 6 star reviews and then read a few 2 star reviews. You will catch on quickly!

As already said, Science Diet is not a very good food; the Taste of the Wild mentioned is an excellent choice!

It could be the issue is not his food, but perhaps a treat? Or, being a beagle, something he finds and eats while outdoors? Because you said it seems random with him being fine for a few days to a few weeks at a time

Getting him on a quality food will be a good first step.