Suggest Remedy For Itchy Skin In Arms 7 Scalp

Dear Doctor,I am a student abroad. I am suffering for itchy skin in general but in one arm and on the same side back it is some kind of small pimple like things in one in 5mm diameter and on the back it is not circular. I remat ccidently itched it, it turned black it is itcy and painful. My sclap is also very itchy and I feel so uncomfortable. There are no lice in my head and I cant see dandruff too. If possible please help me.