hi there, injury to the testicles leads to hematoma formation or hemactocele which may resolve in due course of time . You need to get a ultrasound
of the left testicle done and also semen analysis
to see whether the counts are normal. Usually if the semen analysis is normal then you should not have any fertility
issue but you could always get your self checked by a urologist
to rule out any other problem as you are complainging of continous pain which has increased in the recent times. Do get yourself examined and tested. Take care.