Hello,
You are having spots on the bottom of the feet / sole.  It has come overnight. Commonly, such spots occur due to blisters. Blisters result due to continued friction or 
stress to the skin. You are suggested to get clinically examined by a GP or a 
dermatologist. Get required blood tests and skin tests done. It can also be caused by 
fungal infection like 
tinea pedis and generally occurs on the soles of the foot or between the toes.
Left untreated it can cause 
redness, itchiness, burning, and scaly skin. Get treated at the earliest. Your treatment will depend upon the pathology detected. In the meantime, take care of your foot, give it rest. Do not touch, scratch or pick. Always wear a comfortable pair of shoes. Do not share your shoes, socks, toiletries or clothes as it may cause spread of infection.
Presently, you can apply ointment 
Soframycin on the area affected for relief. If it is itchy, you can apply ointment 
hydrocortisone on the area affected. Stay away from addictions if any, do not walk bare footed for a couple of weeks till it get healed.
Take care. Hope I have answered your question. Let me know if I can assist you further.
Regards,
Dr. Nupur K., General & Family Physician