You should have gotten a notice similar to what is shown in Fla Stat s 77.041. See:
Review the notice in the above link. To qualify for head of household you need to meet one of the following:
a. I provide more than one-half of the support for a child or other dependent and have net earnings of $750 or less per week.
b. I provide more than one-half of the support for a child or other dependent, have net earnings of more than $750 per week, but have not agreed in writing to have my wages garnished.
If you meet one of those tests, you can bring paycheck stubs or tax records as evidence.
There may be other exemption categories applicable. See if there is a Legal Aid office in your county, and give them a call.
To schedule a consultation, call my office at 407-965-5519. I am licensed to practice in Florida only. My answer does not create an attorney-client relationship, nor does it constitute legal advice. Proper legal advice can only be given after learning all circumstances and conducting a comprehensive examination, including being able to ask questions, and cannot be given just from reading one question on an Q&A board such as this.