I don’t like to drink more than one day a week but when I do drink it’s hard for me to stop

Usually I don’t get the urge to drink too often and only drink when I’m out with friends or maybe once a month on my own just chilling on a Sunday night but I find it incredibly hard for me to stop once I’ve started. Does this mean I’m an alcoholic? There’s no really going light for me unless I bought a small amount, if I buy a fifth I’m likely to almost finish it.