Self employment taxes are to be included in "taxes paid last year." For most people, "taxes paid last year" is the amount on 2018 Form 1040 line 15 (except for amounts from Schedule 4 line 59 resulting from other than distributions and certain amounts that might be included on Schedule 4 line 62).
Regardless of where your income comes from, if you have insufficient tax withholding to cover at least 100% of "taxes paid last year" or 90% of your current-year tax liability and a balance due of more than $1,000, you'll have a penalty. To avoid that you might need to make quarterly estimated tax payments to avoid per-quarter underpayment of taxes.
https://www.irs.gov/taxtopics/tc306
