Hello everyone! Girls, could you please tell me who knows: "The sexual…

Hello everyone! Girls, could you please tell me who knows: "The sexual act was on October 19th, two weeks after I took a test and it showed negative. My period started three days earlier than usual cycle. But my period lasted five days longer than usual seven-day menstrual cycle. On day six of the cycle, lower abdomen started to ache and already for two days." What could this be? Thanks in advance for your answers!