My AT&T e-mail inbox is suddenly full of SPAM

I have AT&T for my main email account.  I had the usual filters set up and a spam folder...all were working great...until a few days ago.  I literally had just been on the account just hours earlier.  The first thing I do when I get on my laptop is check my email and then I just keep a tab open as I use it so often. I tend to not sleep much so one night a few days ago I went to check my email and was shocked to see over 700 messages!  Most of these were pure spam.  I saw one I recognized as a pretty good site for tech products so out of curiosity I set up a filter for those...didn't work!  Now, I'm not a tech expert by any means but I can usually solve this kind of issue but I'm at a total loss as to why this happened and how to fix it without having to individually block each address.  I don't think there's even enough room on the block senders list to get them all on it. So I'd really like two answers if possible: why this happened and how to fix it!?

I didn't do anything different, didn't change any settings, etc., and haven't been on a lot of websites as I tend to shop the same ones.