I've heard varying theories on which is more or less effective, and I'd stick with what you have right now and if you're happy, don't worry. The imported domperidone is usually quite a bit cheaper, though.
Some women gain weight on birthcontrol pills, and some women don't. If you haven't in the past, you're probably okay. Any weight you do gain will probably come off pretty easily when you're nursing a chubby babe!
I'd stay on the bc pills for as long as possible. Your babe is due in July, right? Then I'd probably go until late May or early June, or whenever you complete a pack of pills around then. It depends on what you want to do. Pumping for months can be tiring, and you'll maximize possible breast changes by staying on the pill as long as you can.
Good Luck. How very exciting!
Kerri