oh emmie, you have my sympathy. i had it at about your age too, you couldn't get a pin between the spots, it was awful. all i remember doing is spending most of the time sitting in a luke warm bath with bicarb dissolved in it, using a cup to pour the water all over me to relieve the itching. and plenty of calomine lotion when i wasn't in the bath.
how about ringing the surgery for some advice, maybe some antihistamine tablets or cream would help. if you're not going out, it really doesn't matter what you look like, with cream or lotion smeared on your head, just as long as it helps with the itching. poor old you :(