How do you lose water retention from medication?

I've gained a lot of weight since I've been on my meds like 10lbs a month, I used to be skinny, now I'm big, but it's not fat, it's water retention from my medications, and I can't come off my meds, because even if I miss one dose, my heart which is weak, will have arrythmias, and quiver and wobble and pause, so I have no choice but to be on these meds, I don't eat much, I eat pretty healthy foods, will walking and jogging help with water retention, should I talk to my doctor about this? Is there some kind of real medication that helps one not gain so much weight through water retention while on meds? Or is this something that I just have to live with forever, since I can't change these meds ever.