In addition to what others have said already (seriously, see a doctor), it can also help to redirect the urge. If your brain currently demands something to be picked, it doesn’t have to be your skin - plucking on loose threads or fabric fuzz in an old towel until the surface feels smooth again, peeling labels off glass bottles until there is no paper left, anything with “tiny imperfections” that you can remove with a bit of fumbling can help to easen the urge without you damaging yourself in the process.
This is not “the solution” tho - it is only an additional little help to medication and therapy.