Gaining

I gained about 15 pounds (135 to 150) drinking heavy cream for a couple of months. I stopped drinking it, didn't change anything else, but now I'm back to my original weight.

Has anyone had a similar experience? I don't want to have to keep drinking heavy cream to maintain my weight.

How much cream were you drinking?
To me it sounds like you're not eating enough calories without the cream to maintain 150, so if you try again, I'd suggest counting calories to make sure you're getting at least enough to maintain.