Why are medical expenses shown under my deductions, even though I didn't enter any?

Did you enter a SSA-1099 that had Medicare premiums on it?

Any insurance premiums paid that you entered would go under Medical expenses even without you entering them.  

Thanks for answering - I'm filling a 1095-A Health insurance Marketplace

If you did not get or did not get enough to cover your full premiums, this would be the amount showing up under medical expenses.