How do you knowing if a job isn't for you?

Don't quit unless you're offered a new job.

Lot's of people have jobs that are not stimulating. People work for money. If you can find something you think you'd like though, go for it if the pay and location are good.

Is it an unpaid 'internship'? Yes? Then it isn't for you.

Usually 3 months is enough time to decide weather or not you're the right fit.

If you don't like your job then look around for other opportunities and quit when you have another job offer.

3 months is enough to tell. start looking at applying to other companies

Perhaps you should be seeking a paycheck rather than passion or stimulation from a job?

If I were you I'd start looking for something right now. Three months should be more than enough time to know whether you're in the right place or not!