Okay, you have a thread with most of the reasons for chickens not laying presented in it, plus the reasons on this thread as well.
We can't tell you exactly why your particular hens are not laying-no one can do that. One may not be laying for one reason; another may have a different reason. Patience is what you need. Wait it out. Eventually, if they are healthy and well-kept, they'll begin laying again.
I just got my chickens Sayurday 3 of them add 3 more monday and built a chicken coop yesterday( used dog house until yesterday dogs never used it) any ways what is DE and why do they need it, and a dust box. I have no ideal why I got chickens other than was at feed store and decided eggs would be great. Do the nesting boxes need a top on them right now I put sides so all 6 have their own box plus but a 2x4 for them to roost on they slept in next boxes last night. I have gotten 1 egg sunday, tuesday, Wednesday, and Yesterday even with me and my husband building when will the other 5 start laying.
One question I have not seen answered yet is what the OP's chickens are being fed. Also, have they ever been dewormed? Internal and external parasite load's (you mentioned possible mites) will result in unthrifty chickens and decreased laying.
The nesting boxes are inside of a building which has a room the sides were to give them there own space do the boxes still need roofs. Others have said no because of them being inside a building??????????