Hi, Welcome to the Health care magic forum. 
               As you describe, it appears that it may be due to the 
injury or pressure over the 
radial nerve, or triceps muscle, during the delivery of the baby.  
               I advise you to 
consult a neurologist for diagnosis and treatment .
               He may prescribe you injection of 
vitamin B1,6,and 12 for 10 consecutive days, and then periodically. 
               Avoid taking potato, other tubers, tomato,egg, chicken, and sea foods, for few days and observe. If relief is there avoid for some more days. 
               Wishing for a quick and complete recovery. Thank you.