What type of saddle are you using on your bike? Could be your saddle, so you might want to try out a few different ones to see which is most comfortable for you. You're wearing biking shorts w/chamois? Make sure they fit you right because if the chamois is moving around, it'll chafe you. Have you tried using chamois cream? I like Bag Balm---helped prevent some bad chafing in the coldest of the winter months.