What is wrong with me?!!!!?? Night sweats, fatigue, aches, and weight gain!?

I've recently gained 8 pounds, which is odd, I'm a healthy woman 24 about to be 25 next week. I am on my treadmill almost everyday, I'm very active at my job and eat healthy. The past 3 weeks or so I've noticed a lot of nights I am having night sweats. I am soaked when I wake up at night. Another thing I've noticed is joint pain and some body aches here and there. I literally feel like an old woman when I get up from the couch. My hips and knees hurt! When I ran yesterday on my treadmill I just wanted to slouch over and my legs hurt so bad I felt so fatigued. A few years back they found a cyst and nodule on my thyroid (thyroid problems seem to run in my family) but about 6 months ago I had my T3, T4, and TSH all checked and they were normal. I have very bad anxiety and I'm on Zoloft for depression anxiety. My doc's don't ever listen. I'm starting to worry that something is seriously wrong. Can anyone help?