Phentermine for weight loss with PCOS

So my reproductive endocrinologist prescribed phentermine for me to lose some weight before starting Letrozole. I also found out that I have a 1.2cm uterine polyp that needs to be removed. I've read about the side effects of phentermine and so far I haven't had any except for a racing heart for about 45 minutes or so the first day I took it. My question is has anyone had real success with phentermine? I'm curious if it will work as I also have PCOS.