Your UserAuthority (UA) score highly depends on your followers (read more about how it works here), So ever if it suddenly goes up or down, It probably because a influential person followed or unfollowed you.
So how do you know who that person is? Pretty Simple — Head over to steem.makerwannabe.
Enter your steem username in the field, select timeline and click on 'Show Followers' button.
That's it it will show you follows/unfollows and mutes.
Aside from that you can track followings and resteems as well.
There is no need of login or anything like that, you can look up anyone's profile ;)
Made by @shaunmza, not me!