my head is a itchy itchy machine. help?!

everytime i wash my hair on a normal basis every week y'know. condition my hair here and there and wash it out during the week. i have really curly hair and i love it and all. its kinda short like nose lenght lol when i stretch it. i get this itch everywhere around my head no matter shampoos or conditioners i use. every of them seems not to work. iam not allergic to anything. they say when my head icthes,it is normally because it is dirty and has dandroof which i dont find. i wash my hair normally as i use but recently it started icthing for over a year now. ouch ouch ouch. what could be the problem? i dont mind the itch in my leg but on my head makes it more serious!!