I switched from combined to mini pill 2 weeks ago. I've had awful nausea and loss of appetite. Could the change of pill be the cause?

Yes. While all hormonal birth control pills have similar side effects as a class, you may be sensitive to one specific one more than another. Think of it this way: UK makes many wonderful cars that all take you where you need to go but you may have a fondness for one brand more than another, say Aston Martin. Chat w/your GP. Do give yourself 3mo to get used to pill. If persists, discuss options.