no period after I got off BC. Doctor said not good

I had been on the pill for 3 years I finally got off of it and I haven't gotten my period for 4 months going on 5. I had finally went to the gynocologyst and he said it's NOT normal that I should have gotten my period one to two months after I got off. I am so worried now expecially cause he wants to do a ultrasound and I got blood work done. I hope it's nothing serious. Has anyone had something like this before??