I figured out this evening the cause of the low temperature readings. Not leaving the thermometer in my mouth long enough. It is a digital thermometer, and I haven't used it for a couple of years; I'd forgotten that I had to wait for a telephone like string of beeps to tell me that the thermometer was finished. My temperature currently is 98.1, and I sweated slightly from walking up and down the stairs a few minutes ago. That slight sweating fits in with my slight temperature (my normal temperature is about 96.5). This makes sense. If I really had a temp of 91+ I should have been in hypothermia and almost ready to go into a coma. So, the low temp is a non-issue. I didn't take my temperature a few days ago when I was sweating more from moving about, and the temperature then was likely a few degrees higher. Having the temperature come down is a good sign.
I'm still able to go up and down the stairs fine, in contrast to the first 24 hours when I couldn't do that.
Now that the temperature thing is resolved, all of my symptoms point to a simple case of overuse. I did a lot of snow shoveling during the week after Christmas. We had one storm of 6-8 inches of wet heavy snow, and I spent four hours shoveling my driveway/sidewalks and those of a neighbor who was out of town. Then we had several storms of 3-4 inches of light, fluffy snow that was pretty easy to shovel. Also, I spent an hour helping clear my daughter's driveway of 8 inches of heavy snow. All of this would have put stress on my body. During this time I was doing a weekly run of 10 miles and another one of 8 miles -- more stress. I knew I was tired and had shortened the 8 mile run a couple of times. Apparently I needed even more rest, and my body succumbed to the stress with soreness in my right buttock and in my groin. I stretched my buttock, and that soreness was gone after 24 hours. My groin soreness is slowly going away, as witnessed by the reduced temperature, no problem climbing stairs, and being able to walk further before the groin-soreness comes in. Another thing that tells me my problem is overuse is that I feel fine when sitting down, even for several hours of sitting down.
I haven't been doing my groin stretches during the past few days, and I'll start doing them tomorrow for several days to help my body overcome the stress in my groin. I usually do them before each run, but I had skipped them during the runs last week. Having weak groin muscles is not a good thing, because those muscles control the alignment of the knee cap as it moves up and down the knee.