How can I keep my job?

First of all talk to your boss. Let your boss know you are trying the best you can to be a good employee and do a good job. Tell the truth, if you were late because you misplaced your car keys than tell that. If you were up all night with a sick child then overslept your alarm clock tell your boss that. Of course if you were up all night doing shots of tequila with barflys you probably should lie about it then quit doing it!

Come up with a action plan, what are you going to do to rectify the situation? If you boss excuses past problems (s)he will want to know the situation is going to improve. If you don’t have a plan to improve your job performance problems than it is just a matter of time before your problems accumulate to the point where they have to let you go.