I work 12hrs shift and sometimes when i get off i have swelling in my legs, ankle and foot , but after i go to bed and elevate them the swelling goes ?

Leg Edema: Swelling or edema in the foot and ankles is not unusual in folks that work on the feet for long hours. After ruling out things like kidney disease, heart disease, venous disease with your primary care physician you might be a candidate for compression stockings which can prevent the fluid from pooling in your lower extremities.

Venous insufficiency: What you described is a fairly common occurrence. If it is possible to take small breaks during your work, you may wish to elevate your feet during those breaks to prevent too much fluid from accumulating in the dependent parts during standing.

Get a Leg Up.: It sounds like the valves in your veins are beginning to fail. This allows the blood to slowly slip downward causing the edema. Long hours of standing can accelerate the condition. There is no easy solution that is compatible with the type of standing you do. Elastic hose, elevating the feet during breaks may help. It is the effect of weakened valves and gravity, go figure.