What has happened to my Facebook account?

[lighters]

well it depends on many things.
whether you have a slow internet connection
but you said that your sisters account works just fine so here is the trick as you use chrome
1.go to settings and then options
2.the next step will be to click on under the hood
3.then click on "clear browsing data" then check on the box which says " Delete cookies and other site and plug-in data"
4.then click on the drop down box and click "the beginning of time " and click on "clear browsing data.
This will definitely increase the login speed
have fun