That happened with my brothers iPhone, there is no way out of it unless you have Apple Care then you can turn in yur phone and get a new one. But you do have to pay a $49 service fee for that option.
Mine is too! There is really no at- home way to fix this. There is something you can use to fix it MOMENTARILY WITHOUT USING THE LOCK BUTTON!!!!!!
STEP 1: Go to settings.
STEP 2: Go to General.
STEP 3: Click Accessibility.
STEP 4: Scroll down. Under Physical & Monitor, there should be a white box that says AssistiveTouch. Click on it.
STEP 5: Click on. Now, you can turn it off and lock the screen without using the lock button (Which is stuck)! There should now be a little white dot in the area of you screen. You can actually control where it is by dragging it to a corner of the screen. If you click on the white dot and click Devices, you can see that you can do all sorts of things. You can rotate the screen, lock it, turn the volume up and down, and shake it (that's if you are to lazy to change the music)! If you want to turn your iPod off, just hold down on the lock screen icon and it should bring you to the power slider! The only thing is, you have to plug the iPod in (As if you were going to charge it) for it to turn on!
I highly recommend that you go to the closest Apple store. They will help you. The amount of which they charge you depends on how stuck it is. If it is minor, they won't charge you a whole lot. But if they have to take the whole thing apart, they will charge you a fair amount of money.
If they cannot fix it at all, then they will give you a new iPod. That fee will be from $99 to $199! (But for a new iPod that's not too bad. I got mine for almost $300!)
I hope this helped!
Thanks for your advice. I can now lock my phone again!!! I don't have to plug it in to switch it back on either, I just have to press the home button and it comes on to the power slider. Thanks again.