Yes, you have to file a tax return. The $10,350 ($10,400 for 2017) filing threshold does not apply to self employment income.
You will not owe any income tax, because your income is below $10,400. But you have to pay social security and medicare ("FICA") tax on your earnings. The self employed pay FICA as "Self Employment Tax" (SET). SET is calculated on schedule (form) SE and is filed as part of an income return.
You will owe $989 of SET, based on $7000 of self employment.
