Thanks for your query,based on the facts that you have posted it appears that you have pain in left testicle and cord which gets relived on ejaculation.
This is common to have pain in testicle when it is fully stagnated with semen which subsides after masturbation
However the pain in spermatic cord
needs to be evaluated to rule out Varicocele
Please consult qualified Urologist
for clinical examination and get ultrasound scanning and colour Doppler study of th scrotum done to rule out varicocele.