558 is an average score in Neet. You know that the cutoffs change every year so it is quite difficult to predict. Now going by last year cutoffs, it would be difficult to get any government medical college as last year the cutoffs of government Medical colleges of Bihar had the cutoffs score above 580 for OBC category. However you can try for Private medical colleges. You have fair chances of getting into private medical college of Bihar.
You can check the cutoffs here http://medicine.careers360.com/articles/neet-cutoff-bihar
But keep in mind that these are based on previous year data and this year it might change. So I would suggest you to use Neet college Predictor tool to know where you have good chances of getting admission http://medicine.careers360.com/neet-college-predictor?icn=QnA&ici=qna_answer

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