Can u be fired if u call in sick after starting a knew job?

They can fire you for any reason while you're on a probation period. If you call in sick too often, you don't show up for your shift with out calling, you're often late with out notifying your boss are all reasons that they can fire you for.
You have to get some help for your anxiety if you want to work in a buys store. You can't call in sick all the time just because you don't want to work. They depend on you to show up when you're supposed to be there. If you get caught in a lie you could also get fired. If you want the job then you have to show up and go to work.

Yes, especially if you use a lame excuse like that one.

most likely yes, as this is a bad excuse and lying also goes against you

Vvv

that might depend on the policy of the company, they may consider you 'provisional', not permanent and during that trial time, you are probably held to higher standards than when you are a regular employee, so using this lame excuse and calling in sick is a very good reason they don't want you
if you already have anxiety over this job, you best find another one, this won't stop unless you take steps to get over the anxiety on your own

You could but probably won't unless you get caught lying.. But how are you going to handle things ongoing?

I believe so, you should wait a while before calling in and if u have anxiety, u should get a therapist and tell him or her your problems and he/she may prescribe u medicine.

Bosses need no reason to fire you.

Starting to take time off when you've only been there a couple of weeks is a bad sign to your employer. What excuse are you going to use the next time you don't feel like going in? That's not how the real world works. "Anxiety" seems to be the bane of all young people these days. Suck it up and learn to deal with it. If you focus on doing your job well, your anxiety will disappear.

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