Doubts about sonogram

I’m actually on my 3cd and my doctor asked me to have a sonogram around the 3rd or 5th day of my cycle to investigate PCOS. The thing is, during the sonogram, the doctor said I had a “vesicle” or a “sac” in my uterus, but didn’t say anything else about it. I’m freaking out because if its a yolk sac, then I’m probably having (or had) an abortion. The question is: is there a possibility to have a sac inside my uterus that is not a yolk sac? So confused right now :(