Lots of pain in legs

Hi guys, I have noticed a lot of built up pain in my legs, especially the underside of my thighs. This has been going on a while now. It hurts when I push a little on them. I have gotten regular pains before but I have never experienced such long lasting pain before. It feels like it's coming from the muscles underneath. What do you guys think it's from? I regularly exercise but this has never happened before, it's like on both undersides of my legs....