Thanks for your query.Based on the facts that you have posted it appears that you have pain in left testicleand difficulty in getting erection.
The pain in testicle may be due to Varicocele
which is common on left side.
However this can be confirmed only on clinical examination.
As regards difficulty in getting erection it may be due to pain that you have in testicle or may be due to anxiety
Consult qualified Urologist
to confirm the diagnosis.and further treatment.