Can I get stretch marks without gaining/losing weight?

A few weeks ago I noticed a red line that starts exactly at the skin fold where the inner thigh and and the crotch meets and and ends about an inch and a half further along the inner thigh.

It's maybe half an inch wide line and its shape is like if you would scribble perpendicularly along a line. a shape kinda like this..
http://i52.photobucket.com/albums/g11/Fire flash/SMark.png (Not an actual picture, just a Paint drawing of it's approximate shape.)

The color is a dull red/purple. Near the skinfold it's close to skin color (but still visible) while near its tip on the inner-thigh it's slightly more colored.
It's painless and isn't protruding out of my skin. Actually if I touch the area with my fingers I can't really feel any difference.

I'm 29 of average weight. (5'8, 165 pounds) and haven't changed weight in a long time. When I first saw it I though I migh've hurt myself somehow perhaps during sex without noticing. But it's still there, and it doesn't seem like it has improved or worsened over time, although I didn't pay much attention to it. I do sit at a computer all day, if that makes any difference.

I can't find any pictures of skin diseases that look even remotely like what I have. The closest pictures I found were stretch marks but it doesn't make sense for someone my size with a stable weight to get that in only 1 place. Or does it?