[AbiDrew85]

Hi I was just wondering when should I use the progesterone cream?

Start the same day as the last day you use PM and use for UP TO two weeks (could be less, usually less for NBE)

Also, this wont cause me any problems as i'm only 22?

Shouldn't. Most girls are done growing by 21. You COULD potentially still be growing if you're either a VERY late bloomer or a particularly slow grower. But both those cases are exceptionally rare.