The tingling comes and goes, I'm not sure how often, but it is frequently there.
The thumb by itself does not belong to a specific dermatome. For example, C6 would include the index finger.
Nor does it pertain to a particular nerve; carpal tunnel syndrome or one of the other entrapments of the median nerve would affect the thumb, pointer, middle and often part of the ring finger.
So, nothing specific there. Next up, try pricking your thumb with a needle and comparing it with the other hand. Is there a difference?
Now look carefully at the muscles around the thumb; is there any sign of wasting? Does your hand feel weak when opening a bottle or holding a hammer?
Do you have stiffness or pain in the neck and, in particular, if you turn your head to that side, and then look up, does the tingling radiate down to your thumb?
As with any condition, if it's not going away, or getting worse, then it is best to get a professional opinion.
It depends on your age too. At eighty you might accept it as a normal part of aging, but at thirty take it more seriously.
I hope this contributes.
Dr Barrie Lewis DC