Needing advice

Ok so I had a miscarriage starting the 12th of January. It was confirmed on the 21st. My fiancé and I had sex the 11th, 15/16th and the 18th.

I honestly don't think I am pregnant because the tech would've seen it on the 21st but is there any reason why my breasts are extremely tender and I'm nauseous?

Mind you my breasts don't hurt when I am expecting my period or during it. They literally never hurt but they were so extremely tender when I was pregnant. I know there is a logical reason for this. I also didn't really experience nausea this last pregnancy but my one before I vividly remember throwing up cheesy peas.

Is there any logical explanation for these things? I'm thinking the flu or pneumonia! I also don't believe my HCG levels are all gone because I still haven't seen my primary care provider since the 21st. We have been having a terrible winter. And when I went the 21st she found nothing and my uterus was clean. She just wanted to do another blood test.