I live in California and if the work laws are anyway related to your state than your in luck.if you call off sick for a day your ok but if it's 3 or more you WILL have to show proof of doctor note also if it's becoming a habit they could fire you anyway they can. so try and save those sick days for important times because there well be a time you'll mess up and need it.
Being unreliable is a good way to get fired, yes.
It is very possible.Talk to your supervisors.
your job is in jeopardy because of your irresponsibility