I think my gosling is constipated

I have 3 gosling who are maybe a month old. My husband bought them at a feed store out in town. Today my husband noticed that one of them seemed to be straining to poop but nothing came out except green discharge and clear liquid that I'm assuming is water. He/she keeps straining hard and kind of jumping up and down. We tried mineral oil, put he/she in the bath tub with warm water, wrapped them up in a blanket and used a heating pad set on low to help them feel better. Nothing has worked at all. I have it in my room in a big crate because we didn't want it going out with the other geese until we know it's OK. We have had chickens for years but new to geese so we are stumped. Any advice is appreciated.