Hello,
Sudden appearance of a rash is indicative of viral infection, contact dermatitis or an allergic reaction. You can apply some calamine lotion at the rash as it will help in soothing the skin. You can take some OTC oral antihistamine medications like Benadryl or Claritin and see if it helps.
For mild-moderate symptoms a weak steroid may be used (e.g. hydrocortisone as dermacort), whilst more severe cases require a higher-potency steroid (e.g. clobetasol propionate, fluocinonide).But they are available under prescription and should be taken only after consulting a dermatologist. Please get it checked by a dermatologist to confirm the diagnosis.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
You should have a doctor look at this rash to make sure that it's not something other than an allergy to something. It could be Shingles, which is related to the virus that causes Chicken Pox. Shingles can start out just like you described. If this is Shingles, you will have to reduce contact with other people to prevent the spread of it. The idea that someone who has had Chicken Pox is immune to it is false. I know this from experience. This is something you cannot delay in seeing a doctor about. You need to go now. Call your doctor and get an emergency appointment for today. If there is nothing, go to the urgent care clinic or go to the emergency room. You have to be evaluated to ensure this is not Shingles and to get treated right away. If this is Shingles, you aren't going to like the Valtrex anti viral side effect of nausea. Since you will need to keep contact with others to a minimum, you will need to just take advantage of this and take it easy. If you can got to class or to work online, do that, but take it easy. The Valtrex will make you want to take it easy, too.
Also, go to the Vitamin D Council website for information about how much vitamin D and magnesium to take. The magnesium is crucial for the vitamin D to work. If it's Shingles, it wouldn't hurt to follow the suggestions they offer about taking the higher doses while having a cold or flu virus temporarily for just a few days. After that you should take a minimum of 2,000 IU - 5,000 IU daily like the website suggests. It's not an unreasonable amount. I actually take the 5,000 IU daily just for maintenance because that's what my body needs.
You should get your vitamin D tested, but I doubt very much anyone in the ER will do that. Your doctor might or might not. But, you need to see the doctor TODAY.