Thanks for your query.Based on the facts that you have posted it appears that you have
sustained trivial injury to your left testicle due to vigorous prolonged sex with your girl friend.
However final diagnosis can be confirmed only on clinical examination by a qualified General surgeon
In the mean while start taking pain killers like Bruphen 400 mg twice daily which is freely available over the counter.
You may need to get Ultrasound
scanning of the scrotum
done to rule out Torsion of the testis.Further course of action will depend upon clinical findings and Ultrasound report.