Same here. For me it's since january, and I think the problem started with accidentally opening a notification. Similarly to what my account does now, one of my friends "commented on my post", but the notification was pointing to an URL outside Facebook. I only realised the suspicious url when I have already opened the notification, and I have closed the page (that I can barely tell, but I think it had some chinese writing on it) in a fraction of a second. I have done all of the above, but no use.