You can't calm down because you have something on your mind and can't find a good solution, so these things are bothering you and lingering. You can make a list of things that bother you, rank them according to the severity you think, and then solve them step by step according to the severity.
Maybe there is no good solution to these problems after you think about them yourself. You can ask your relatives and friends for advice, but it's useless. You can consult a psychological counselor and negotiate a solution.
If most things that seriously affect your mood are solved, then your heart will naturally calm down!