What Is Causing My Lower Legs To Swell Everyday?

What is causing my lower legs to swell? Every day I put on 2 to 3 pounds of water and every night it goes away. I take 1000 MG of magnesium daily, potassium, A, B, c,D,E, Calcium, Milk thistle. I eat very healthy. I walk 4 times a week for 45 minutes on a 3.2 mile walk. I am worried and frustrated. Do you have any more suggestions. It was suggested that it could be the limbic system.