Is there anyway to raise your blood pressure?

I have low blood pressure and often faint, especially in the shower. I went to my doctor yesterday and he took my blood pressure and said it was low.

I'm not underweight or overweight. I have Chronic Fatigue Syndrome and Fibromyalgia as well. I eat healthy and drink plenty of water.

Any suggestions?

Thanks.
I'm on B12, I have been diagnosed with depression and I drink more than 8 glasses a day, normally 9-12 glasses of water.