Less space while defraging, help?

I'm on Windows Vista, my hard drive is 150gb.

I have been using defraggler for years with no issues. Recently I realized I hadn't defragged in a LONG time. I mean like months. So I figured I'd let it do it's thing. I started it defragging and left it overnight. When I woke up the next morning it was still going, ok no big.

When it finally finished it said it had cleaned up about 30 gigs of crap. Woohoo, yay me. But within a couple of days this was full again. I hadn't downloaded anything. I hadn't deleted files, moved them. I really hadn't done anything other than piddle about on the internet.  I didn't understand why this happened but no big.  Tonight I decided to let it defrag again thinking it would clear the problem up.  I started out with 15 gb of free space (so it said) , 12% free.  It is now defragmented 49% and I have 6.1gb free, 4%. 

It has not finished the defrag, but usually the amount of free space I have goes up not down.  So I'm a little freaked out. Also I tried googling the problem and keep reading about shadow copies? But I'm an uber noob when it comes to this sort of stuff. Does anyone have any idea what is going on? How to fix it? What the heck are shadow copies and is it possible that is my problem? 

PS. I'm pooped, and tired of worrying over this thing. I'm off to bed and I'll check it again in the morning. If this is normal feel free to have a good laugh at my expense and say so.    Night y'all <3

I've seen this happen a few times myself, and usually after defragging and a fresh restart, it fixes itself. Try restarting your computer, and then checking the space afterward. If that doesn't fix it, then I have no idea.

I feel like it goes up because it has to move things around but idk how defragmenting works lol.

So Moo it's like playing fifty-two pickup in a small box with many decks. It gathers all the cards back together in order in their respective decks, neat and tidily organized as opposed to the previously thrown-about state, and places the decks back in the box in the least space-consuming way. It tries to reorder everything efficiently, so it should create more room, though I recall a member here (Roph?) saying that he used defraggler and he went from 15GB to 10GB or something.
Not to derail the thread, though. Also I've had this installation for probably two years or more now, and I've never once defragged it...should I? Aside from making more space, what does it do?

I've seen this happen a few times myself, and usually after defragging and a fresh restart, it fixes itself. Try restarting your computer, and then checking the space afterward. If that doesn't fix it, then I have no idea.

Did and it fixed it... weird o0

So Moo it's like playing fifty-two pickup in a small box with many decks. It gathers all the cards back together in order in their respective decks, neat and tidily organized as opposed to the previously thrown-about state, and places the decks back in the box in the least space-consuming way. It tries to reorder everything efficiently, so it should create more room, though I recall a member here (Roph?) saying that he used defraggler and he went from 15GB to 10GB or something.
Not to derail the thread, though. Also I've had this installation for probably two years or more now, and I've never once defragged it...should I? Aside from making more space, what does it do?

I mean I know what defragmenting does, but I don't know how it does it. I guess I was kinda vague on that.

This has happened to me every time I used defraggler.

Without inside knowledge of how these tools actually work I would expect that to reduce the risk of data loss they first copy entire files, checks for errors in the new file which may be a crc check and bad sector check, and first then frees up the file at the old location. Moving the file block by block is simply to risky.
So I find it hardly surprising that the size goes up during the process.

It is also possible that the file system index for some reason becomes messed up and reports a different total amount of free space available. You can check this by going to the root of the drive, selecting all files and right-click->properties. It may take quite a while for it to finish counting. (Make sure you can see all types of files, hidden or not)
Should the size be vastly different from what the drive say then that indicates the presence of file system index problems. You can use the error checking tool to check the file system for errors. I have seen that fix the wrong space left problem I once had after a defrag.

*hugs*

your hard drive is imploding.