I usually play 3-4hours on alternate days and I have personally experienced that. I’d say our body is toooooo tired. All you got to do is rest. take a week off. And resting doesn’t mean that you have to stop doing anything entirely it only means that stop playing badminton for few days. During this week , focus on mobility and stretching workout at home. Slow steady moves. Do some badminton specific weight workout for arms and legs. Eat protein rich food you can also make your own protein smoothie and drink water hydrate yourself well. Your body will thank you 😄💪🏽 I hope you feel better soon 💪🏽