Found a sparrow 3 days ago. It's not moving anymore. What should I do?

Three days ago, we found a young, medium-sized sparrow. We (my family) built it a cozy little house. We gave it male larvae from a beekeeper in the village. We fed it the larvae we got with tweezers (NOT METAL, but plastic, because that would hurt it). Theoretically, there should be enough water in there, but we also held out glucose water for it with a pipette just to be on the safe side. It didn't look injured. We found it when magpies attacked the nest. I think we were lucky. The first day, it chirped all day and hopped around in its cage, which doesn't look the same today. It rained all day, but when the shower stopped for an hour and we wanted to try to see if it could fly, it only flew 3 meters, after which it just chirped on the ground. Today, it just sits in its cage and looks very weak. We've always given him food and water regularly (about once a day). He still doesn't move. Does anyone know what could be causing this?