I have a lot of issues with my intestines - they have been badly affected by these infections. I get this fairly regularly, but I have to admit that I have never noticed the pain going down into my thigh - but it's been going on for so long for me, that it could be and I'm not paying any attention to it.
Because you had a colonoscopy not long ago, and things seemed fine then, you can likely assume things are fine now - for those things.
As you can see in this interactive body map here:
www.healthline.com/human-body-maps this would be the lower large intestine, which would have been very visible during the colonoscopy.
If it keeps happening, I would encourage you to call your LLMD and have a talk about
it, but if it only happens a few times, then it is likely safe to assume that it's your intestines reacting to the treatments.