LH surge with no AF??

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I was having a ton of ovulation symptoms so I took an opk and got a positive. I was so excited that my cycle may be returning. Well here we are 19 days later and there is no AF and all negative pregnancy tests. For a week now I've been having period like cramps along with other PMS symptoms. I'm so confused. Any thoughts? 
Also, the opk I used was digital so I couldn't have misread it. Maybe an LH surge for another reason?