Why am I not getting my period!!

So I haven't had my period since December. I had blood tests for PCOS and thyroid and everything was fine. I'm not particularly stressed and I changed my diet to see if that would help as well. My doctor keeps telling me just to keep track of it and we'll come back to it but I'm 27 and I really would like to get pregnant and this certainly isn't helping anything. Has anyone ever had this problem? Any supplements or anything i can take to get things moving?