low sodium

I have fibro and have had it for years.  I have suffered so much until my doctor put me on a new Drug
called Savella.  It has helped me so much.  I take 100mg, twice a day, and have been on it going on
2 years now.  I also have mild diabeties and was taking 1000 mg of metformin twice a day, until recently.
I decided to lose weight, so in August of 2010 I joined Nutrisystem, and have lost 35 pounds.  I now manage my weight with weight watchers and eat allot of their meals.  
Now with all of these good things on my side, my blood pressure has gone up and my sodium is so dangerously low.  I am going through allot of test, but now my doctor has decreased my savella to once a day, and I am in allot of pain again.  
Has anyone here take Savella?  If so, any side effects for you?  We are not sure if it is the Fibro medication, and I am so afaid that I will be taken off it for good.  Any advice???