Hi. This appears to be a really rare case. Very rarely heard of. The possible reason can be development of a varicocele, which needs to be confirmed by an examination by an Urologist in standing and lying down position and to be supplemented by color doppler examination to prove or rule-out this. This can give the pain as you explained. There is going to an increase in intra-abdominal pressure resulting in Back-pressure in the veins which drain the testis area.