Noticed a small bruise and swelling last night on my scrotum. today it is almost all black and tender. should i wait for it to go away or see a doctor?

Here are some...: Without a direct look at it, but based on what described, this bruised swelling could represented infected sebaceous cyst forming an abscess on its verge of spontaneous bursting. If not running chill & fever, not feeling sick, and being healing, you may wait out & let nature take its course for now. If still in doubt, seek evaluation soon. Besides, such a cyst (if yes) may recur even after healing