Respiratory Diseases in Poultry

I have 10000 layers which have been ill for almost 2 months...they have CRD and Mycoplasma gallisepticum infection. After they got infected with pox and then IB infections., we treated them with tylosin, doxy, timulin, amantadin, avilosin, linkomycin and oxytetra, etc.....but after 2 months mortality is 15 / days....we stopped all medication but still mortality...pox is also present...what can I do? Bird age is 7 months