Bring stock, fish sauce, salt and sugar to a boil. Add ham and chicken. Simmer for 15 minutes. Remove chicken and shred. Return to pot. Beat egg with fish sauce and saute, make into a thin omelet. Add shrimp for the last minute of cooking. Slice omelet into strips. Add noodles to the soup and simmer for 3 minutes. Add omelet shreds, scallions, bean sprouts and shallots. Serve.