Is it normal to have 1"x1/2" left testicle? twice as small as the right. what could be the cause of this? could this cause low sperm count?

No, not normal: Average testicle size after puberty is ~2" long, 0.8" width, and 1.2" height (5 x 2 x 3 cm). Causes of a small (atrophic) testicle include: 1) painful conditions like torsion, infection, and severe trauma, and 2) painless conditions like the presence of a varicocele, abnormal development, genetic anomaly, prior surgery affecting blood flow, steroids, etc. Depending on cause, could affect fertility.