I can only answer this question on two counts I wasn't in Poland during the war.
I was in Germany,so may be able to add some facts about this which may(or may not) be similar to Poland.
When we arrived in Germany,we found a brothel (usually) in each town,however these were run by German madams and were for the German Military and Non~Military population,but were obviously not staffed by "forced" girls.
As slinky cat says there WERE "forced" brothels in the Concentration Camps,these were staffed by inmates(predominantly Jews,but not exclusively)It seems it gave German soldiers,both Military and SS etc a "kick" to be(in effect) raping a Jewess!(my wife's dead cousin was one)
As I was attached to SOE,we often got classified information,that was for one reason or another,not seen fit to divulge to the world at large.(Then or later)I couldn't have told you this 25 years ago.(Now it is de~classified)
One of these files was data on "forced" brothels set up the German Military in occupied countries.As I say I was never in Poland,but it did come into a file that I had seen,regarding such brothel setups.
As will be obvious as Germany was occupying Poland most "normal" brothels closed down.So the senior members of the German forces took over various large houses (in effect Polish Castle,Chateaus etc) and rounded up scores of (good looking/pretty) Polish girls to service the German soldiers.This is why the castles/chateaus had to be in the middle of nowhere,as it prevented the girls from running away.Don't imagine tha these brothels were for the ordinary soldiers.Oh no,you had to be officer rank and upwards to take advantage of them.Despite being in what were(usually) luxurious surrundings,the girls were kept under close guard in prison like accomodation.I haven't seen evidence of a "lower level" of forced brothels for the ordinary troops,but that doesn't mean they weren't there.