Diet pills and missing period

I have recently been taking a diet pill (Hydroxycut) for the past month or two. Last month my period was a smidge late, but it came, now this month it's been a week since it was supposed to start and nothing. I'm currently trying to do herbal remedies to persuade my uterus to bleed, but I don't know what's going on. pregnancy isn't really OUT of the question, but the two times my SO and I had sex during the "fertile" window, he didn't even finish. I have taken two pregnancy tests (First Response) on two separate days, both negative. I was just wondering if anybody has had problems with their period while on a diet pill. Also I have a lot of anxiety and stress about literally everything, but it has never really been that much of a problem in the nether. Any and all info is appreciated.