TBsNana, that was me earlier on this year, was convinced all the time that I had Covid, and was constantly on the phone to family and friends for reassurance. I did do a test but it was so stressful that I messed it up and in the end did not send it off, and I have not been tempted to repeat the experience.
Unfortunately this all developed into full-blown health anxiety, and I seem to have had the surgery on speed dial! Everyone has been very patient with me, and referred me to hospital for tests to set my mind at rest. My GP also recommended a course of anti-depressants, which seem to help. I can imagine what TBsNana,'s DH is going through, and it is not pleasant. I became too scared to go beyond the end of my road in case I met anyone, but can now happily go for a long walk without wearing a mask, and have conquered my fear of the hairdresser and the optician, and have even been to a couple of garden centres. Still not been in a supermarket, or on a bus, though.
I had a course of CBT, which taught me a few strategies for dealing with my fears, and I can now think rationally and put most of those feelings out of my head. A thermometer is a good idea! Happily I have not felt the need to check my temperature for some time. Although my optician automatically checks your temperature on entering the shop - last week it was 35.2!
You just have to be patient, as the fears are very very real, and just try to explain why he cannot possibly have the virus until it eventually sinks in, as it did with me in the end.