My upper thighs are very itchy, and there are these weird raised red lines/bumps... what could it be?

I have no idea what's happening to me down there! My upper thighs, right near my buttocks but not actually on any skin that would be covered by undies, are so itchy. There are these strange red raised lines and bumps on them, almost like what you'd see when you have sat on some wrinkled fabric-covered thing for too long and it's left marks, or like what you'd see when you've scratched yourself and the skin is raised as opposed to broken (but a little bigger.) It literally could be from anything, because I recently went on vacation to NYC where I visited family and wore shorts doing all sorts of outdoor activities, and then drove 20 hours home in a car (I do remember at one point feeling itchy in the car in that spot and figured I'd just been sitting in one place for too long on the leather seat.) I was in multiple houses, multiple beds, sat in grass, and have been wearing clothes that have been in a suitcase for two weeks.

Any thoughts? Weird thing is the itch is intermittent, sort of like how a mosquito bite's itch is okay until disturbed -- but when it is irritated it's much itchier than a mosquito's bite. When would I know I should see a doctor? It's only been about two days so far. It's mostly just weirding me out right now.