Admin backlog is inevitable for freelancers. Emails, invoices, follow-ups - the list in general can be difficult to keep up with, especially when working alone.
The easiest way to keep on top of work is to write things down. Sounds like a no-brainer? It is! But it is possible to not do it, especially when multi-tasking and in between non-related work chores.
But use a list anyway, whether through an expensive software, Excel, a fancy phone or by a free corporate journal (which is what I use), make a to-do list of what needs to be done and keep it updated every single day.
There is no satisfaction like ticking off tasks, even the most mundane. With every tick, freelancing management gets a little better.