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The only way to be sure you have actually ovulated is to either have a blood test or to chart your temperatures throughout your cycle.
It is possible to experience more than one LH surge during a cycle before you ovulate, so the best thing to do is keep having sex every 2-3 days throughout your cycle. Sperm can live up to 5 days (extreme end of the scale) inside your tubes but the egg will only live for 24-48 hours.