I need your help ladies.

I have been riding in my Sidi Raiden's ever since I started riding (I even used them for spin class before I got my first bike). When I go for rides that are less than 2 hours, my feet don't hurt and the shoes are quite comfortable. But anything longer than that...and my feet are killing me. The first time this really affected me was when I rode my first century. I thought it must have been the hot weather that caused my feet to swell up more than usual, but towards the end of it, I was in so much pain, and when I got off my bike, I immediately had to take off my shoes.

Same thing happened to me today 3 hours into my ride, and it felt extra painful where my cleat is located. When I took my shoes off, my feet were throbbing. It seems to happen more when I do lots of climbing.

Are my shoes simply too small? Do my feet just swell up so much after a prolonged time on my bike? Are the soles not hard enough? Cleat in the wrong position? The rest of my body doesn't hurt in that "my bike fit is off" kind of way.

I'll use any excuse to buy new shoes, but I need to know if I should buy them half a size bigger than what I currently wear.

Thanks in advance!