My work life is falling apart

I am months behind in my work. I can't stay on top of my workload. There are so many moving parts. Reports to write, phone calls to make, emails to send, planning to do, appointments with clients. I make to do lists but they are long and overwhelming. I forget to go back and update them. I end up with multiple lists.

It takes me so long to do a simple task cause I overthink it. My days disappear and I've hardly achieved anything but feel like I've been working all day.

I feel terrible because I tell clients and colleagues I will do something and then never do it or do it months later. Please please help me with strategies. I am so desperate to do better.