Why am I so angry all the time for no particular reason?

So I am a 20 year old male who is turning 21 next month. Sure, I just left an incredibly abusive job environment, but other than that, I have nothing to be upset about. I have plenty of money, I have a girlfriend, I have lots of people who love me. But you’d think since i quit that job, I’d be feeling better right? But I’m still not, and even in happy times there’s always this subtle anger inside that invades my mentality. Does anyone else experience this? If so, what can I do?