TRACON Controller reported being unaware of issuing clearance below the MVA with read back error. Controller reported fatigue due to staffing and scheduling was a contributory factor.

Narrative

I have been super busy outside of work (moving) and doing a lot of things before and after my shifts where normally I'm able to relax. Also we have been extremely short at the facility; so it's pretty normal to be working 6 day work weeks instead of 5. I was extremely tired before I took the Sector and almost considered taking sick leave. But I thought it's ok; I only have a couple more hours to go. The aircraft departed CRQ VFR and requested an opposite direction approach at ZZZ (VFR weather). They weren't accepting ODO because of staffing. Aircraft X then requested an IFR clearance to CRQ (marginal weather). I had the pilot climb to the east VFR and gave him IFR when I decided his sequence. It was a slightly busy with multiple IFR arrivals/departures; but not that complex.As I was issuing the approach clearance; I noticed that the Pilot appeared to be descending below the MVA (3500 ft. in 3600 ft.) so when I gave the clearance to join final I restated 'maintain 3600 until established'. The Pilot came back and stated I had issued him 3300 ft.. I said no I think maybe you confused the heading 330 and maintain 3600 ft. The Supervisor checked the replay and I had issued 290 heading at 3300 ft.The 3300 ft. MVA is the next MVA; but I never give that altitude until I'm turning final.Now I don't remember issuing this heading or altitude. It's something that we do so repetitively I don't understand why I would give something different. I think since I was so tired; I was on auto pilot. I wasn't concentrating on the readbacks and obviously was giving wrong instructions to pilots in a sector that I've been working for years. I ended up taking sick leave because I was pissed off that I had made such a small mistake. But also if I can make a small mistake like that; I can make a bigger one.I am back to work today on my 6th day.I wish I could say a recommendation would be that we don't have to work so much overtime. It's frustrating that we are behind in hiring and there is no light at the end of the tunnel. I'm sure the continuous OT has caused some consistent fatigue.My life outside of work has been so busy with the move that I haven't had adequate down time. I should have tried to spread out everything I was doing so I could come to work refreshed. I definitely should have gone home sick when I felt tired instead of trying to pull through. I think so many times we do just pull through and work tired because it's something we are used to (with quick turns; OT; etc).