I’ve Had Blood Work Done And All My Hormone Levels

I’ve had blood work done and all my hormone levels are normal. This includes my estrogen, progesterone, LH, FSH, testosterone and all thyroid hormones. I also appear to have no cysts after 2 pelvic ultrasounds. My period refuses to come and it has been almost 4 years. I started my period when I was 11 and I am now 17 going on 18. I’m worried I may have a pituitary tumour since all my hormones are at normal levels and I have no cysts. I have been given Provera to induce the shedding of my uterine lining but I want my periods to come back.