Though I rarely experience loneliness, I do tend to go through phases of being more or less social. In my case, less social means virtually no social contact with anyone for days or even weeks, and more social means a few phone calls. I rarely actually see the people I know face to face, mostly for geographical reasons.
People are exhausting in many ways. Even a phone conversation can wear me out, especially if I'm already stressed or fatigued.
I have noticed that my AS seems worse as I get older. Now that I'm 40+, I am acutely aware of how socially far behind I am compared to age-equivalent peers. This sometimes bothers me, but I know I cannot do anything about it, so I find the feelings of frustration fade.