Suggest Remedy For Persistent Headaches

my 14yr old son has been having headaches since feb of this year. we have been back and fourth to the doctor. MRI came out fine. They have been treating him for migraines but no medicines are working. He went for a physical and we told his primary doctor that he sees about this and he starting feeling the top of his head and it was very painful for my son when he pressed down on it. He said it counld be some swelling because he had him to lay down and my son felt pressure and these headaches are only early in the morning. He put him on presdisone and he has been on it four days now. How long does medicine star to work for his condition?