My Husband Has Diarrhoea From Friday/Saturday Early Morning. I Sought

My husband has diarrhoea from Friday/Saturday early morning. I sought advice on Internet and he has been eating banana yoghurt vegetable soup potatoes and keeping hydrated. He cannot fast due to the various medication he has to take for rheumatoid arthritis, diabetes, atrial fibrillation. His excretions are now bright green liquid ? Should we continue to wait for nature to take its course or seek medical help. He says he feels weak but not as ill as on Saturday. We have just come back from Spain (flew sat) he has been bitten by mosquitos. Could this be related atall ?