Stretch marks even though I didn't put on weight?

I put on 10lbs over the winter (like I always do), but now I've noticed I have three very faint stretch marks on my right hip.

Problem is I didn't get bigger there; my tummy grew a tad and so did my thighs.

What could have caused it?

It doesn't make sense to me. I'm only 113lbs, and as far as I know a usual 10lb weight gain shouldn't cause stretch marks.

Any idea why they're there?
Stretch marks even though I didn't put on weight?
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