I got Covid again

Hey guys I’m just posting this because I’m honestly so confused on why I have this virus again. I had it back three months ago with no symptoms and I had tested positive and then went back a few days later to retest and it was negative. I got fully vaccinated not too long after that. This week I was feeling sick. I was getting symptoms of a common cold but I took a test just to be sure and low and behold it’s positive. While the doctor was swabbing my nose yesterday he told me the chances were so extremely low because I had it already and its hard to get Covid twice and I have the vaccine. I’m just so confused and on top of that I was supposed to go on vacation next week.