Both of my legs feel as if from knee down are hurting... as if, my bones are being nawed at, or just ringing with pain.. what's wrong with them?

I haven’t done anything really, i remember that when i was about 6 or 7 years old, i experienced this same kind of pain, except the pain was all over my body. Now i’m experiencing it again, but only from my knee down to foot. It happens every so often, about 2–3 times a year. Is something wrong with them? The last time it happened was when i wasn’t used to standing up for over 8 hours, my legs felt as if a numbing pain was inside my bones. (very hard to describe… >_<) That was just this summer. And now i’m experiencing it again. I was standing for 4 hours straight only. Why is this happening.. is it linked to something that could be more serious? I’m not sure if it has anything to do with standing too much, just thot it might help if i say what i was doing before experiencing the pain. I stand all the time, but this doesn’t happen too much. it’s constantly in pain.. and has been like this for about 6 hours now. I’m sure it’ll probably be gone after a day or two, but should i look into it more?

Last year, I felt this pain at a random time, I wasn’t standing too much either. It just started hurting and i remember not being able to fall asleep because of that. Like always, the pain will cease after a day or so.. but… is that good enough? I don’t want to make it such a big deal and have a doctor check it if it’s nothing much. It’s definetly not the kind of feeling after you’re legs are tired, or overworked. Just.. a ringing pain inside my legs.. =\