One month my period is very severe and now it's not even here?

Last month my period was one of the worst one I had ever had. It was so painful I could not walk nor do anything except lay in bed. Also the pain got very sore to the point were I started vommiting (which is rare) I never vomit like at all. I ended up having to go to a&e and they gave me period medication. It's been 35 days since my last period and mine usually comes after 21 days. I haven't had sex since January so pregnancy is out. Any suggestions as to why my period isn't here
One month my period is very severe and now it's not even here?
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