Could I be pregnant ?

Hi everyone ok so I’m scared I may be having a cryptic pregnancy. So in July I had sex, he had a condom on but then took it off and did it for less than 5 mins. He did not cum at all! But I’m scared there was pre cum but i am not sure. I took a plan b pill but I didn’t really need to take it because I had already ovulated. I got my period when expected after that but ever since my period had been kinda off and came at different times. However it’s been normal heavy blood like usual. I took a pregnancy test and it came negative. But lately I’ve been feeling nauseous so I’m scared this might be a sign. Please help me !! thank you!