Hi,
I've just spent about a month's wages on a pair of Brooks Glycerin 12s. When I put them on in the shop and ran around a bit they felt great, really cushiony and supportive, but now wearing them around the house to break them in I'm getting really achy arches. Should I stick with them or have I bought the wrong shoe? I bought them because I want to start to train for a marathon next year and I couldn't go any further than 5K in my Nike's without getting debilitating blisters

These say they're for medium/high arches but I don't know what I've got? The woman in the shop did a gait analysis and everything so they should be ok, but I'm worried I've spent loads of money just to have painful feet and still not be able to run a marathon! These are my first proper running shoes so any advice from anyone that knows what they're talking about would be great