also many browsers have a privacy mode that does not retain information like login data (such as Chrome's incognito mode, or Safari's private browsing). make sure you aren't in that mode unintentionally. if you are using such a mode intentionally, thats a tradeoff youll have to make.
Thanks for the info but I checked the box to "remember me" and no problem for a while now. I've checked that box now and then before, I just didn't remember to do it this time.