pokemongo

I am pretty new to the game and I’m trying to figure out how people keep track of what’s going on. I’m not trying to do everything, but I’d really love to know my options are.

It seems like info about events/raids, etc. is kind of a mish-mash of official announcements and infographics made by random people. I saw today that all the raid pokemon have changed, but I’m not clear if that happens on a schedule or if it’s mostly a surprise or what. Are the infographic people getting leaks or something? Is a single info source wishful thinking?