Sharp pain on leg as if hair was pulled but much stronger

[Marscaleb]

Every now and then I've felt this pain on my leg as if I were pulling a hair. I never thought much of it; it seemed to me that I got a hair pinched by my pants somehow.  I'd rub or scratch the area, sometimes the pain might flare again, the pain would die down, and eventually fade away and I'd forget about it.  This happened from time to time, across several years I think.

But just four days ago it happened again and it was far worse than I have experienced before, and it's been happening at least once a day since.  The pain is very sharp.
It certainly appears in connection with my pants rubbing against my leg, particularly "against the grain" of my hair.  It can be more noticeable when I pull my leg up higher, like walking up stairs.  It also seems to be stronger when my cell phone is in my pocket, as it rubs against the same spot.  In all these things it feels like I have a hair that gets caught in the fabric and gets pulled, except that it has become far more painful than pulling a hair.  Also just trying to brush the area to free the hair does nothing; the next step I take the pain surges again like it were still stuck.  And the area still feels very sore for the next few minutes.

There is nothing visibly wrong.  The skin looks completely normal; no redness nor any hair that looks abnormal; I can't even pin down the exact spot by the time I can take off my pants to look.  I used my beard trimmer to cut down all the hair in the area, but I still get this pain.