Yo buddy.. I've been in the same situation with a total of 36 DSC done, not a single exotic drop so far. Also, remember that the exotic weapon only drops on FRESH runs, which means you can only try one character per week. Maybe next season? But don't feel bad or demotivated, one of my friends had around 60 conclusions of last wish to get his one thousand voices. May the Bungie bless your RNG buddy!