If you plan on being a working artist, keeping inventory records is an essential component of your business. When I started painting, the idea that I would someday have an inventory that needed managing seemed rather remote. It really wasn't until I first started putting work in shows, and selling work, that I realized how important it would be. Almost immediately upon my entering work into multiple physical exhibitions, things got confusing.
There are a lot of art inventory methods out there and I am not going to pretend I evaluated them all, I did not! I happily fell into using Artwork Archive about seven years after I started painting -- just enough time to have quite a lot of work to add. Over the past years the developers at Artwork Archive keep adding features, which serve to make my business run much more smoothly.
Inventory tracking systems aren't a substitute for a good website and well-organized personal files on your computer! So do get organized, and get some sort of repeatable system under control. No matter which method you settle on -- even if you start by keeping lists, or a spreadsheet -- track your work. Give it a name, write down the dimensions and medium, the price, and give it an inventory number (especially if you use inventive names like 'Untitled I'!)
And record that same information in some fashion on the back of your work, to close the loop!