You can check your activity log and see if you have sent any requests in the past(you may have to go many days back; Click on "More" and then filter as "Friends" from left panel). If you see anyone unknown, go to their profile and cancel the request.
Also there may be, unknown imported contacts and periodic reminders are being sent to those contacts on your behalf. You cannot retract the sent invite but you can remove the imported contacts and prevent any further periodic reminders from you.
Nothing should be able to send friend requests on your behalf. I would suggest that you do the following:
Check all devices you use to connect to Facebook for malware.
Once you are sure all devices are clear, change your password.
When you change your password, you will be asked if you want to logout of all places where you remain logged in. Make sure you choose to do so.
This should stop the problem. You might also want to set up alerts if someone logs in from an unrecognized browser.
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