Answer: If all numbers can be used as many times as wanted then there are 109 = one billion combinations. If each number can be used only once, there are 10!/(10-9)! = 10!/1! = 10! = 3628800 combinations.
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Clearly answered by someone who does not know the difference between PERMUTATIONS and COMBINATIONS.
The combination 123456789 is the same as the combination 213456789 etc. All in all, therefore, there are only ten combinations which use each digit at most once.
Answer: You need to see a doctor. It sounds like Irritable Bowel Syndrome, or ciliac disease, which is caused by an allergy to gluten, especially wheat gluton. It interferes with the normal absorption of nutrients in the intestines.