Your crotch is on of the hottest areas of the body, so sweats excessively. You may have focal hyperhidrosis which is a disorder where you sweat excessively in specific places of the body. The main causes is genetics, but it can be many factors including climate, stress, puberty, diet and obesity - here's how to sweat less
Yes it is normal. Your crotch is a closed area like your arm pit that will hold in the heat and cause you to sweat heavily. Also heavy back sweat is normal.
This is because your crotch, arm pits and head generate the most heat. That is why these three locations sweat the most
I am guessing you are a female by the profile pic, but the person who answered you question is right.Also, when I exercise I have to wear a panty liner because while I'm exercising by bladder will leak like when doing jumping jacks.
Try to go naked at home and get some air and sunlight on it.