If I am taking the new Yaz pill is there any reason why I can't take diet pills? Like could they cause me to get pregnant easier?

No, you wont get pregnant easier as they are not antibiotics, BUT you want to be careful regarding your fluid intake as Yasmin already has a diuretic in it and diet pills often do as well. If it has ephedra or large amounts of caffene, you'll want to ensure you're drinking plenty of water or you'll end up with headaches, dizziness, and being nauseated.