It's pretty hard to push yourself into significant detrimental effects from overtraining, but it seems like you could have done it.
MOst chronic overtrainers go to the gym for like 2-3 hours at a time.. maybe 6-7 days a week.
That's not as heavy a burden as you would get if you did multiple workouts a day though. It's much more taxing doing that because you can "refresh" then come back harder. Single sessions are quite self limiting to some extent.
In fact, that's pretty impressive that you could beat yourself way far down in <4 months like that. You must have had some preexisting conditions or likely a combo of multiple workouts a day plus some poor nutrition and/or poor sleep and overstressing from other stuff.
Seriously though you need to take off for like 4-5 months like I did.