The right front brake started skidding?

The brake pads and rotors were replaced 1 month ago. The calibers were not replaced so the brakes were not bled. Twice while pushing hard on the brake at a stop while adjusting my position on the seat I heard a popping sound, and the brake pedal dropped a little. On a different day while slowing down for a turn on a dry road the right front brake started skidding this has happened also when coming to a stoplight. I have had the brake pedal go almost to the floor and had to pump the brakes once to get the car to stop. I have not found any leaks and the reservoir is full. If you have any suggestions, it would be greatly appreciated. Thank you