What Causes Progressing Red Marks On Upper Inside Part Of Thighs?

I have a few red marks on the upper, inside part of my thighs. The largest one is about an inch long and a quarter inch wide. The other marks are very thin and almost like lines and some are more like blotches. They're red, to pink, to almost purple in color- they seem to change color depending on when I look at them. They don't hurt or itch. They aren't raised up above the skin- they actually seem to be indented. I've had them for at least a month, and there are more of them now, and some have gotten bigger. I'm sure it's not a rash, and pretty sure they're not stretch marks. Any ideas of what they could be?