47 years old, weight gain of 7.5 lbs in one week without changing eating habits and swelling of ankles have taken pristiq (desvenlafaxine) for 4 years?

Swelling & wt. gain. Wondering if the wt. Gain started after you started the pristiq, (desvenlafaxine) and if you are taking any other medications that can affect your blood pressure & heart/kidneys. I agree with dr. Pappas to get pcp evaluation.
Please see doctor. This is quite a bit of weight to gain in one week. Combined with swollen ankles, this makes me wonder how your heart and other things are doing. This may not be related to Pristiq (desvenlafaxine) at all, but something else -- and this deserves a close review with your primary care physician.