Random Review wrote:sometimes it is helpful to think of "aber" as "however". In the long term, I reckon it's best seen as neither, but rather as a discourse particle in this kind of use. German likes these little words (eben, doch, etc) for expressing subtle discourse meanings. You should make a study of these on their own terms.
I am not an expert on German by any means, but I think this is very helpful. Possibly the OP may not have thought explicitly about these very different uses of 'aber'. Note for example: 'Und ich brauche ganz dringend eine.' but definitely not '*Ich brauche und ganz dringend eine.' - 'und' doesn't have the 'discourse particle' meaning.