I experience similar kind of pain when I don't have the footbed support I need in my boots - I need extra arch support and correction for pronation.
Pretty much if I am aware of any "empty space" between my foot and the insole I know I will end up with cramping... the support for my foot has to be correct. Likewise in a boot that is too narrow I end up with similar pain. Funny thing is, this doesn't bother me as much in street shoes, but my cycling shoes showed very clearly where my foot was not making any contact with the insole, and I was having arch cramping on my bike, but changing the insoles fixed that (I still don't make complete contact, but the pain is gone, which is good enough for me).... I think it has to do with the rigidity of the soles, so street shoes don't bother me because they bend, but my cycling shoes have very stiff soles - not unlike skate boots.
In terms of going to a fitter vs fitting yourself.. really all a fitter is going to do is listen to what you say about how your foot feels in a boot and suggest what you can do about it (try different size, different width, different brand, etc). A good fitter will have a variety of boots and sizes to try, but that doesn't always mean that you will end up with better fitting boots, it just means you have a better opportunity of getting it right, and the possibility of making it right if they get it wrong (if they boot ordered doesn't fit).