The classical history increase in size in left testicle followed by shrinking to pea is indicative of problem-related to the testis only.
It looks that you had a torsion of the testis which was not diagnosed. As both the arterial as well as venous blood supply gets permanently blocked the tests very easily goes into atrophy hence the finding which you have.
You can get this confirmed by ultrasonography and consult Urologist for further treatment if need be.
Hope this helps.
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