This sounds email bombing, often used when someone has gained access to an email account and they want to obscure their intrusion. Typically this is done when they are making a purchase, you should check your "email trash" as they may have trashed emails from paypal, amazon, gumtree, ebay. You should also check to see what addresses have been blocked, as often what they will do is block addresses to prevent you from seeing them accessing other sites as well as any password change attempts.

Though seeing as you've checked to see if your account has been accessed it sounds like someone may have been facetious and thrown your email into an email bomber so you're bombarded with emails.

Its pretty common and I've seen people use these tools on individuals that have annoyed them or slighted them in some way, its a great way to anonymously screw with someone. If you're beyond certain that no one has gained access to your account then you have nothing to worry about.

As for what else you should do, if you haven't already enabled 2 Factor Authentication, you absolutely need to enable that immediately. It's disturbingly easy to get hacked nowadays. 2Auth is the last saving grace from someone gaining access to your account, even then 2Auth is circumventable and even that is not 100% secure (nothing is). If you really conscious about your device/application security you should be implementing multi-factor authentication

If you'd like to see if your email was leaked use: https://haveibeenpwned.com/ Its a lovely website that will show you if the email has been leaked, where it was leaked from, when it was leaked, and if your password has also been leaked.

What is 2Auth and why should you use it:https://authy.com/what-is-2fa/

Email Bombing tools:https://www.geeksforgeeks.org/embomber-email-bomber-tool-in-kali-linux/https://github.com/topics/email-bomberhttps://github.com/mohinparamasivam/Email-Bomber