Sour Milk

I woke up this morning, actually about ten minutes ago, and grabbed a bowl of cereal (corn flakes). I have a feeling that something is wrong with my milk though... but, I can't really tell. Yesterday, I had a suspicion because it tasted kind of funny but today, something definitely seems to be wrong with it. It doesn't taste like normal milk, HOWEVER it doesn't expire until September 14th. I don't understand what happened or why it tastes this way and living on my own is not supposed to be this way.

(thanks mom)