It's an amphetamine, right? They tend to metabolize very quickly, within a couple days if I'm not mistaken. I don't know if you have regular cycles or not, but here's what I would do to play it safe. If I were in the pre-ovulatory stage of my cycle, I would prevent through that ovulation, wait for AF and try again. If I were past ovulation, I would TTC after AF.
But as bad as stimulants can be for your health, I think you would probably be OK if you got pregnant this cycle too. I don't think amphetamines have been shown to alter chromosomes or do any other obvious damage to your eggs or developing babies (although I'm not advocating using them while pregnant or anything.) Good luck! | 
pregnancy and phentermine??? 
