After you file

You could amend your 2015 return to include them.  But be aware that the medical expense deduction is very hard to get.  If you were under 65 in 2015, the only part of your medical expenses that even "count" are the expenses you PAID that were over 10% of your adjusted gross income. And then you also need to have enough other itemized deductions to exceed your standard deduction.
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