Importing meta data from Discogs ID when there are 3 Disks of a CD

Hi and thanks for me joining .
I have a couple of CD boxes [3 CD] that I've ripped to Flac and they only have 'Track 1 flac' up to 15 as the file name.
I tried for the first time to use 'Tag Sources' and I went for 'Discogs id number'
The problem is that I can only tag the first CD -When I put CD 2 in ,the same results appear as for CD 1.
I can't find a way to get Discogs id for EACH separate CD,though I'd of thought there must be the individual id's somewhere?
Would I have to rename all the tracks individually in Mp3tag ??
Also when I selected save on the first CD it saved successfully but in the right pane it still called the filenames 'Track 1 flac' etc,but when I played the file in Winamp,it had indeed named them so then I opened it up again in Mp3tag and after selecting 'Edit' the filenames were still listed as 'Track 1 flac' etc..
Is this normal or am I doing something wrong there?
Thanks for reading and any help would be much appreciated and meanwhile I'll try to find individual ID's for disks of a set in Discogs...
Cheers all!