Let’s talk HCG

Give me all the info you have about HCG levels... I know they have to double every 48 hours roughly. But my questions are:

1- would they still double if you were having an ectopic pregnancy?

2- would they still double if you were miscarrying? But just because they aren’t one day, doesn’t mean they won’t stop at any time and then be a miscarriage right?

3- how often do you get your hcg levels checked?