Joint Pain?

I've been having some pretty awful joint pain lately. It's mostly centralized to my lower back (just above my tail bone/at the base of my spine -- it feels a lot like I need to crack/pop it, but no matter how I turn or what I have people to do help, nothing will crack it), but travels often to my hips and my knees. There's no swelling or inflammation that could suggest an infection, but it's been hurting like this for around four weeks now and nothing (not heat or any over-the-counter pain reliever) seems to help. Earlier today, I was walking and my left knee just kind of gave out and got weak all of a sudden, and couldn't bear any weight. I felt a little bit of pain in my hip, where the bone goes into the socket, and my knee. It didn't hurt as much as I expected it to (what with the rest of the joint pain), but just trying to walk on it made it buckle and I had to do a shuffling limp kind of walk just to get to a chair. The pain is mostly achey and dull, but it sometimes throbs. It doesn't move around much. On a scale of 1 - 10 with 10 being absolutely unbearable, it ranges from a 6 - 9.4 on a day-to-day basis. Often, the pain is accompanied by weakness in my legs that kind of feels like it travels from the tops of my legs down to my feet and almost feels like they're sliding off (sorry for the poor description!).
I'm young (fifteen), and am fairly sedentary because of school. My mom thought it might just be growing pains, but this has been going on for around two months with no height changes and my doctors have said I'm about done growing (it might be important to mention I have a congenital endocrine disorder that affects my growth, so I started growing/developing super early and super fast and will likely finish growing before most people my age). I was also diagnosed with chronic migraines a couple of years back and had a particularly nasty flare-up two weeks ago (a migraine around the same time every day for about a week and a half) but those have since decreased in frequency.
Not sure what could be going on. I've tried to see if my mom could take me to the doctor, but she doesn't seem particularly keen on that idea, so I figured I might see if anyone had any thoughts about what this might be.
Thank you in advance!