There were red spots/rash at the tip of all of my fingers and some spots on my palm and on the side of my feet. when you press on them, they hurt and blanch. after having a sore throat, high fever, and headache, what could've caused this?

It is good that your fever is down. With a painful rash, please see your pediatrician or internist for an exam and a good history. Rashes are notoriously difficult to diagnose via text based questions.

Hand-Foot -and-Mouth Disease is usually associated with viral infections in children 4 or 5 years or less. Though one is 18years, the associated symptoms listed, fit this. Most of the time it resolves on its own enabled by supportive efforts like Vitamin C, Hydration and avoiding cold foods and cold drinks. However if symptoms persist a visit to PCP is encouraged.

You should see your doctor for evaluation. There are relatively few infections that can cause your symptoms. Recently there seems to be an increase in hand foot and mouth disease caused by coxsackie virus. This is usually a childhood disease but it is being seen recently in adults with greater frequency. It can be airborne as well as transmitted by virus in the popped blisters.