Why would I have large dark stools, then small very pale white stools?

[WadeCol]

I was using the restroom, and it came on very quickly, but when I went first I had 2 very large brown stools that came out quickly and easily enough, then some sharp pains and a lot of pressure and about 10 mins of sitting, then several very pale almost white stools. This was a lot more than my usual go, they are usually pretty lengthy, but never different colors with different size/textures and completely different colors.