Insulation in the attic
Karen, this type of question has come up several times.  The basic answer to to provide better ventilation and assure there are no water leaks.  Humidity will collect in any attic that is not properly vented. It can condense on rafters, roof sheathing and insulation, then drip. As you are seeing, mildew and mold will result if moisture is trapped.  If the problem does not improve after the venting situation is corrected, then you may have to consider replacing the insulation.   Mold can cause health problems, an air mold spore test may be a good idea. If any toxic molds are present, remediation will be required.  DO NOT ADD any more insulation over the existing insulation until the venting and mold tests are done.