I need help!

Question
QUESTION: I bought a bearded dragon about two months ago. In the begining everything was fine until my beardy started twiching and having seizures. I did some research and found out that it might be because it wasn't getting enough calcium so I started putting calcium on all its food crikets, mealworms, etc.. Everything went back to normal. He eats well now and he seems happy, but lately he has been acting weird. He twitches sometimes and when he walks its as if he didn't feel his back legs. He can move them but most of the time he's dragging them behind. Also his tail looks a bit wavy and at the very tip of the tail looks dried out and has a dark color. There is no foul smell but I just don't think is normal. If it is please let me know because I'm freaking out. Just to reasure he is eating well and seems happy but this couple of issues are freaking me out.

ANSWER: My first thought is Metabolic Bone Disease or MBD.  What are you doing about UVB lighting?  Does he have one, is it uvB (the B is the important part), how old is it?

---------- FOLLOW-UP ----------

QUESTION: First of all thank you so very much for replying so quick. As far as the UVB I do have one on his tank as well. I bought it at PETCO; I have a basking light too. The temperature in the tank is always between 80 and 90 degrees. At night I always turn off the basking spotlight and leave the UVB light on. Now about his age I'm not really sure how old he is but Im guessing about 8 or 9 months. He is about 7 or 8 inches from the tip of his nose to the tip of his tail. I just want to know what can I do to help him get better?. Im I feeding him properly?, Thank you again for your help.

Answer
If the UVB bulb gives off visible light it needs to be turned off at night.  They need day and night.  If the UVB bulb is older than 6 months it probably needs to be replaced EVEN if it still gives off light (the coating which gives o the UVB wears off).  I don't know what you are feeding him exactly so I can't comment as if it's right or not.