Low in energy and the will to do things - ideas please?

I've been very low in energy for several months. I want to do more gardening for example, but though I have the desire, I can't seem to muster enough energy. I spend a long time in bed reading in the day. I wonder if this is simply an age thing - I'm 73 this year. I have type 2 diabetes but otherwise fairly healthy for my age. Ideas welcome, especially if you are my age or older and have gone through the same thing.