If you're in marketing you know a lot can come at you at once. Deadlines never seem long enough and if you're successful, the work just keeps coming. The key to managing workload and stress is having a few good tools on your side. Here are some I've used that have made a huge difference without breaking the bank.
Wunderlist - A simple, online to-do list that I use every day, multiple times a day. Track tasks by client, by project or however your brain works. The free version is enough for my (syncs with my phone and calendar) but if you want to collaborate with others they offer upgrades at modest fees.
FunctionFox - An essential for an agency, this time-tracking tool is my lifeline for billing. Track time by client/project, adjust rates by situation or role, enter billable expenses, even track non-billable time just so you know where it goes. I've used this tool since 2011 and wouldn't choose any other, especially at the price.
Constant Contact - With plenty of email options on the market, you have a lot of choices. For most of my projects, this one works just fine, and is highly affordable. I use it for client work as well as pro bono. It makes list management and results tracking so easy, especially since you can integrate with Excel.
WIX or Strikingly - For website design, both are incredible tools, especially for non-programmers. This site was built in WIX but I've used Strikingly as well. Strikingly tends to get a few more nods for its SEO but WIX is so easy I literally built a site last weekend for a pro bono client and we're up and running!
Microsoft Excel - What?! Yes, simple Excel. Sometimes you don't need to get fancy when simple is enough. I use it to track just about everything in my life from taxes and revenue to project timelines and mileage. If you fear it, don't. Here's a great online tutorial site that will have you creating Pivot tables in your sleep! https://www.excel-easy.com/
Hope you find your groove and the tools that allow you to be happy in it!