I'm playing the X-Box 360, and I've noticed something strange. When I cast a spell my magicka bar doesn't appear.

it doesn't show me if I've lost any mana, in fact I don't lose any mana, I keep casting spells indefinitely and nothing's coming up.

is this a glitch, is this upposed to happen?

Nope the magika bar should show and deplete when used.
Is the Health and Stamina bars showing up?

yes,

I just got done witha battle, all I did was literally hold down the healing spell continuously while holding down the frostbite spell and at no point did the bar show up or a message saying "you do not have enough Mana" appear.

Mayhe playing at easiest difficulty? Try starting a new character and see what happens
Are you using scrolls or anything? Maybe wearing something with an enchantment?

It's an effect you got somewhere, look in your magic menu at the active powers thing. I had it too, game was very easy during that time, after it went away, it got considerably more difficult.

hmm, well the only one that seems out of the ordinary is this "fortify Magicka 100 points for two hours" effect I have. I have no idea where I got it from though. I also havea robe that does 50% mana regeneration, but when I took that off it still didn't come up.