See a doctor. Numbness is a neurological symptom, face and arms suggest brain and spinal cord are involved, imperative to see a physician for a thorough neurological examination. Seeking detoxification is also important. Iv drug use is notorious for medical complications. There maybe very harnful impurities in the drugs you are using.
See your PCP. Iv drug use, especially of cocaine, amphetamines and methamphetamine, has been associated with a variety of syndromes which involve inflammation of small blood vessels (vasculitis), which can effect nerves and cause numbness. In addition, it can increase the chance of blood clots, which can go to the brain and cause these symptoms. Get help with stopping, and talk to a health care professional now.