rash and Cloxacillin sodium

I got a rash after using a different shampoo but it dissappeared after a few hours. the next day the same thing happened. on the third day i woke up with a rash all over my neck, shoulders, and a little bit on my face. they are little red bumps but they are not itchy, they just feel a little bit warm. i went to a medical clinic and the doctor gave me a perscription for cloxacillin sodium. i took my first pill on the monday night and then 6 hours later. i woke up with the rash on my face apparent even more, and sometimes a little bit itchy but not really. it has now been 2 days of using this antibiotic and the rash is still present and not at all going down or fading. am i allergic to the drug or immune to it?

please help..