P.W.
I take a probiotic every single day ALL THE TIME. Probiotics offer your stomach the healthy bacteria that it needs to create a healthy environment. Immunity begins in the gut so besides helping your digestive system taking that probiotic will also help boost your immune system. Choose a good probiotic. the good bacteria in the probiotic needs to reach your stomach alive to be beneficial. The one I take is triple encapsulated to ensure that. Another thing to consider for you since you have stomach issues is a prebiotic. Prebiotics feed the healthy bacteria to help them flourish. Shoot me any other questions if you like. I sell supplements for a living.
Be Well!