I have filed single head of household with the earned income & child tax credit but this year is significantly lower than usual. I made less but it seems wrong still

There could be several reasons your refund is less this year than last year and everyone's situation is different.  Many employers withheld less this year than they did last year when the tax laws changed, meaning you got more in your paycheck than at the end of the year for your refund. 

Basically, your refund is calculated by subtracting your tax liabilities from your Withholdings, Payments, and Credits.

Your tax liability is calculated based on your 2018 Tax Rates and other liabilities such as Self Employment Taxes or penalties.

Your withholdings and credits consist of what your employer withheld from your wages, estimated tax payments you made and refundable and nonrefundable credits.

You made less so you may be in a lower tax bracket. If so, they withheld less. You may have also had changes in eligibility for tax credits and deductions, changes in filing status or dependents, and changes in the amount held from your paycheck or tax payments made will all affect your refund.

The Earned Income Credit is like a bell curve.  It starts out at $0 then increases as you make more until you hit the peak and then drops back down to $0 when you make more. You may have been closer to the peak last year compared to this year.

To see the exact reason your refund has changed look at your 2018 Form 1040 and compare it to your return from last year.  This year's form has changed quite a bit, so you will need to compare item to item instead of line to line.

Start by comparing line 11 (Tax liability) to your Tax liability from last year. You will also want to compare line 16 (Federal Income Withheld) line 17 (Refundable Credits..Earned Income Tax Credit, Additional Child Tax Credit, and American Opportunity Credit) to last years credits.

Other lines you may want to compare would be line 7 (AGI), 8 (Standard or Itemized Deductions) and 10 (Taxable Income) to last years numbers.

Looking at these numbers will explain why your refund is less. 

To see your 1040 you can click on Tools>>>Tax Tools>>>View My Tax Summary>>>Preview My 1040

If you would like to adjust your Federal Withholdings you can use the W-4 calculator to help you figure out what changes you would need to make to increase your refund. You can do this by clicking here W4 Calculator