My Vitamin D Levels Were Low. So My Doctor Told

My vitamin D levels were low. So my doctor told me to start taking Vitamin D3 over the counter.
After taking vitamin D3 everyday 1000UI I was feeling better than before. I was not as depressed as before. But suddenly I started having low blood pressure. Not too low but lower than usual. I started feeling dizzy and imbalanced. Since past week I started having brain fog and my blood pressure is in normal range. I already had 3 times brain fog and my doctor does not do anything about it except prescribing me an anti-depressant. Can there be any relationship between vitamin D3 and the brain fog. I know vitamin D reduces fat in the body and since the brain is made mostly of fat is there any relationship? I'm really disappointed from my doctor because he was at least suppose to give me a referral for a CT Scan so I don't worry about anything like a tumor in my brain.