Noticed it yesterday when I ran (tried) up the stairs. It hurts the same today as well. I lifted weights today and experienced no pain at all, only when I try to run or jump rope.

It could be a muscle knot or a pulled muscle in the sciatic nerve. If it's a muscel knot or pulled muscle, it could take 1-3 weeks to heal. If it is the sciatic nerve it MAY take up to a month before it heals, depending on how you treat it. If you sit around all day; it would make it worse, so I would recommend slowly trying to stretch more often.

Pains or discomforts in the sciatic nerve could be caused by carrying something too heavy (or even holding a backpack on only one shoulder for too long, since holding bags like that tends to curve your back) or even how your matress or pillows when you sleep are. If it's an old matress, the pain could be from the matress wearing out. If it's the pillows, try and get one that is known to support the head when sleeping like this one: http://arc4life.blogspot.ca/2009/05/sleeping-comfortably-when-you-have-neck.html

Hope one of these help! Best wishes :)