No you can actually Amend 2015 return until 4-15-2019 (three years from the due date).
So 2015, 2016, 2017 and 2018 could be Amended right now.
However for you to take additional medical you must be able to first itemize and then it must exceed a certain percentage (7.5% or 10% based on your age) of the Adjusted Gross Income on the return.
For more details on Medical deductions please see below.
https://ttlc.intuit.com/replies/4774889
