Exercise and fitness is not only good for you health. It is good for the brain too. Exercise means a stronger supply of oxygen and blood to the brain, which is where the ideas are produced and all the intellectual work happens. Quite simply more exercise = more oxygen and blood = more genius.
Exercise does not have to be strenuous and backbreaking. Ir cab be gentle and meditative, like walking, of slightly strenuous, lime cycling. Much on the time spent walking and cycling can be spent about thing the problems you have to solve. Often like magic, sit down after a walk and the problem is suddenly solvable.
Don't take the car. Cycle instead. Don't take the bus. Walk. Over a period of months you will notice an improvement in the clarity of you mind and you grades that will surprise you.