I've heard that most health are professionals don't recommend getting the doppler as it can give you false assurance. It's difficult to get it to work correctly on your own and might pick up your own heartbeat. If by "don't feel pregnant" you mean no longer having symptoms like nausea, that's to be expected in the second trimester. If you're still very worried, it's more helpful to move your gynae appointment than to get a doppler :)
No effect. But I heard many mummies saying it isn’t very effective