I doubt that you caught something from your classmate. More like dry skin or stress. Diet can play a huge role as well as possible allergies. Check for new detergents, soaps, dryer pads and changes in diet.
Stress can play havoc on your body. Don't dismiss it.
I just posted a question, sound similar to you, but i have actual bites! But I get the same prickly feeling you are describing and I was wondering about some sort of body mite also....read my question, look what I have been through!!!
Itchy skin that isn't accompanied by other obvious skin changes, such as a rash, is most often caused by dry skin (xerosis). Other conditions cause itchy skin as well. Skin conditions like dermatitis, scabies and hives, internal diseases like liver and kidney disorders, diabetes, iron deficiency anemia, irritation and allergic reactions to chemicals, wool, soaps, cosmetics and certain foods can cause itchy skin.
You can apply an anti-itch cream or lotion to the affected area. Oral antihistamine, such as Benadryl can also be used. You should take a comfortably cool bath and wear smooth-textured cotton clothing. You should choose mild soaps without dyes or perfumes and use a mild, unscented laundry detergent when washing clothes, towels and bedding.
Please take a second opinion from a dermatologist if the symptoms persist. He/She will start with the specific medications. If an internal disease is found, whether it's kidney disease, iron deficiency or a thyroid problem, treating that disease often relieves the itch. Lastly,Phototherapy can also be tried.
I hope it helps. Take care and please do keep me posted in case you have any additional doubts. Kind regards.