Ringer/alarm volume

I got an iPhone 11 and I have never had a problem with the “change with buttons” option with my past iPhones, I would turn it off and set the volume and never have to think about it again. Suddenly now I do that and I’m constantly having to turn my volume slider back up because it managed to slide itself down to lowest spot. I have been sleeping through alarms day after day because I can’t hear my alarm going off and I don’t understand how it’s moving itself to the lowest setting since I shouldn’t be able to change it with my buttons and I never go into settings to turn it down. I rarely use do not disturb and vibration only. If someone could help me out or at least let me know if my phone isn’t functioning properly that would be great, thanks.