I have the exact same problem (on the right side) and I agree with all the helpful responses so far, and this may seem too simplistic but regular washing of my bibs/shorts makes a huge difference for me. I cannot explain why (perhaps washing restores the padding/chamois to their original thickness/shape?) In my case, I have also realized on long rides the seam in some bibs seem to drift into a place that causes this problem and I need to adjust my shorts from time to time during the ride. Hope you get it solved as riding is really enjoyable when you do not have to endure the burning and painful sensation from this kind of friction issue, and it can be a real pain in the you know what when not resolved!