Our Male Cat Was Throwing Up Clear Liquid For Day

Our male cat was throwing up clear liquid for day and 1/2 took him to vet he checked him over Temp , No Throat obstruction feel stomache are No hardness and cat urinated on the way out in cage all semmed good per vet ? Vet gave him shot for upset stomach and shot of fluid under his skin and said is he is not any better to bring back in. Got Cat home couple hours after we got him home he eat food seemed fine , but now 24 hours later he back to the way he was before ? Not sure what to do ??
Phil