LOTS could be affecting your range. From allergies, to age, to hormones, to using it less, & beyond. The voice is just like every other part of the body... Overuse will hurt it. Underuse will make it "flabby." And to me, it's a matter of doing what I can (allergy meds, gargling tonics, drinking water) and then just getting up and doing my job/calling of ministry.
My voice is definitely showing its age. And it IS a sad experience for me. But, in my life there's nothing for me to do but get up and give it my best. So, that's what I suggest you do to!
Don't get overly concerned, but do what you can. Then enjoy what it is. It doesn't have to sound "like it did" to be of value.
Each stage of our life and voice is meant to contribute what it IS in the present, not the past. What you bring is beautiful when combined with what everybody else brings.
That's my philosophy anyway. Hope something of it is helpful!