Sore knees??

Hi guys -

I'm on my third week of FB Fit and loving it. However, yesterday I did a lower body HIIT workout and my knees are pretty sore. Well, my whole upper legs are sore, too. Is it normal for knees to be sore too or Is this a sign that I'm doing something off/wrong? I'm 26 y/o and weigh 127lbs so I'm assuming its from working out and not due to age or weight. Anyone have advice?

TIA!