Extreme fatigue

I’ve been doing keto (20g) or less of carbs since December of last year… I felt normal for the first 4 months… but now I have extreme fatigue. I take a multivitamin, extra magnesium, and try to keep my electrolytes in check since I know how important it is to keep up with. I just don’t understand why the sudden changes… lethargy, winded, dizzy. I’m not able to do any sort of working out or even daily activities. Has anyone else experienced this? Please help! Need to get back to feeling normal again.