I do understand your genuine concern and anxiety
due to the constant sore throat
problem your child is suffering from. A runny nose and sore throat indicate an upper respiratory infection
. The same infection can seep down and affect his vocal cords resulting in inflammation and subsequent pain. Cracking of voice is a natural phenomena as he is going through his period of adolescence but this per se does not strain the vocal cords. So your child needs an ENT consult wherein the vocal cords would be examined to assess degree of infection. Following this examination ,he can be started on a week long course of antibiotics. Serratiopeptidase
might help in bringing down inflammation of the voice box and bring only temporary relief but will not eliminate infection. So to sum it up, controlling the infection will bring relief and maintain his interest in singing.