Keep trying. It is still very early, you never know. QR

does release new availability as time goes by. 

They do have a City Tour if you have more than 4? or 6? hours layover.  That tour used to be free,  now charges a reasonable fee.  When we flew DBX-DOH-BKK-HKG a few years ago,  I specifically made the DBX-DOH early enough to allow us to take the 6pm City Tour.  They did not leave the airport until 7pm,  returned to the airport about midnight.  We went straightly to the Sleep Room at Al Sawa since our DOH-BKK was in A380 F.   Unfortunately the cabin was filled up by a Qatarian shriek and his family 2 days before the flight,  so all 6 seats were taken... 

Our Nov tickets MIA-DOH-AMM route were booked just one day afrer we already ticketed a MIA-DCA,  IAD-DOH-AMM that I actually called to add the MIA-DCA part after reserving the IAD-DOH-AMM online.   Then a day later QR suddenly released some seats from most US gateways.  I was able to put the new reservation on hold,  canceled the existing tickets, then booked the new itinerary.

So you will just need to keep checking, and ponce as soon as you see anything comes up that works.  Then optimize the routing as long as you see better options.