You probably got keylogged.
Did you download/install suspicius softwares recently?
That sounds like a good theory. You said you had done some mining. I wonder if the keylogger was hidden in software related to mining. I say this because there are a lot of trojan mining products out there. It makes sense to be suspicious of any bitcoin related software because the bad guy can target people who are likely to own some BTC.
Anyway, sorry man. I'm afraid it is probably gone.