It’s important to at least talk to a lawyer who’s experienced with child support, so you don’t let a lot of time go by without filing a motion. It can also be helpful if you don’t know what the calculations are or how they work.
Even if it’s just a consultation, if you spend an hour with a lawyer, you can learn everything you need to know, such as what you need to file and what kind of documentation to bring with you when you’re pursuing, or fighting against, an order for child support.
After an initial consultation, you may be able to handle the child support situation without a lawyer. The calculations are done for the most part in a routine fashion using software.
That said, there may be something unique to your situation where a consultation with a lawyer, and possible representation would be a good idea.