Who had to buy new pants because their legs were getting bigger?
The first time I noticed this was some months ago. Now it feels extreme: I tried multiple pants, swimming trunks. All are getting tight and stretchy.
I don‘t go to the gym, sprint is mediocre at best. FTP around 3w/kg. I started cycling three years ago and legs were normal in the beginning.
Not sure if it belongs into the results category. 
Yes, it happens!
Back when I was racing, I liked Levi 501 button fly jeans but had to switch to some weird larger cut because that’s all that would fit.
Those are the only pants I ever had a problem with.
Happened to me too! I increased from my bike volume to 8+ hours and started lifting heavy in the gym (3 sets x 5 reps) once a week and within 6 months I started having fit issues. I used to wear slim fit pants and shorts and now I need regular/classic fit or it looks like my clothes are painted on. Depending on the brand, I still have to go up in waist size to have something fit me in the hips.
I wouldn’t change it though because I love riding and lifting.
I’ve never had this problem.
But I am sure that’s because I only wear regular/traditional/baggy fit 
I’ve been road cycling for about 45 years by now so nothing to compare to, but finding pants that fit well has always been challenging when the glutes and legs are well developed and the waist is slim.
Skinny jeans are not your friend. I’ve also got boxer undies that the leg won’t fully extend.
Keep in mind your thighs will change shape on season/ off season as your muscles/tendons shorten or lengthen
I buy pants by knee / leg opening.
This is an older thread but it might be helpful: