I have bumps/marks just like those. My docs (all 13 of them) told me not to worry.
I not only have them on my thighs but also my butt, upper back, lower back, shoulders, stomach, chest, calves, and feet.
they just seem to pop up. I get nervous each time i see one. They dont hurt though....not one bit of pain.
These bumps for me may or may not be releated to a yeast infection I have after using very powerful antibiotics for 3 weeks (to knock out a urinary tract infection that spread to my testicles and kidneys)