I Am 54yr Old Female...I Have Not Had A Period

I am 54yr old female...I have not had a period in almost 3 years. My doctor said that after 1 year free of periods I would be done with all this. We'll last night during sex I started bleeding profusely . I bleed for 2 hours before going to ER got there and waited another 3 hours before being seen, by that time the bleeding was more like a regular period. I am still bleEdina as if I am on my period. Dr. At ER said to see my gyn. Is it possible to start my period again or could it be more serious. ER Dr had blood drawn said white cell were a little elevated but the rest was normal. Pleas Help.