Could I be pregnant

Last month I had a very strange AF a total of 2 and half days, and had came 2 days early. I had given up and just focused on this month, I'm in the middle of opk and getting highs, no peek yet, but I'm feeling nauseous and just want to sleep. A thought came to me could I be pregnant from last month? I had taken a test the day after it had stopped but it was neg so I left it at that. I was going to just wait and see if AF comes this month but just wondering if its possible or would the opk not show a high if I was?