How to overcome my resistance to lecturing?

I am in a situation where I have several adult students for an all-day career training program that runs for about a year. So, they and I sit in the classroom most of a normal work-week. I decide when to get up and lecture. Although I tell them to raise questions any time, they rarely do unless I ask.

I enjoy speaking in front of the class, but because it is not on a particular schedule, I usually find that I have trouble motivating myself to get started. I don't have employee reviews or a mentor. My feeling in class is similar to how I have never gotten used to making phone calls: every time it is like jumping in to cold water, it never gets any easier. (I would rather talk in person. I am almost 50, by the way, and male.) How do I get beyond this basic motivation hurdle?