What do you mean by "Medicare is being deducted as well?" Deducted from what?
[Edit: I see that you may be asking about Social Security benefits being paid to you. If so, see tagteam's answer and disregard mine.]
If you are self-employed, TurboTax prepares Schedule SE to determine your self-employment taxes and includes the amount in your overall tax liability determined on your individual tax return (Form 1040), so your self-employment tax liability is determined when you file. To avoid quarterly underpayment of taxes, though, you likely will need to make estimated tax payments (Form 1040-ES) so that your overall tax liability for the year is covered. If you used TurboTax to prepare your 2018 tax return, TurboTax would have offered the option to prepare Forms 1040-ES based on the projected income information you provide. TurboTax does not provide any way to make the actual payment. You either mail a check with Form 1040-ES or make a online payment, say, with IRS Direct Pay:
https://www.irs.gov/payments/direct-pay
If you are an employee who receives a W-2, your employer deducts Social Security an Medicare taxes from your pay and the employer pays these, generally with Form 941.
