Welcome to HCM.
could be due to variety of causes. Since it is of mild nature most likely it could be due to tight inner wear. If you ride two wheeler, that could also cause testicular pain, by tightening the pants and inner wear and pressing on the testis.
Both the testes need not be at the same level. One of them usually the left one hangs a little lower and that is normal and nothing to worry about. If the pain still persists you need to visit an urologist
and get a Colour Doppler Study of scrotum