I'm 30 weeks and 3 days. No matter how long I sit or lay down, when I get up to walk, my inner thighs up closer to my vagina are sore. I still work everyday. But that's so I can have a easier labor.
It is completely natural to feel sore anywhere on the body, and have aching muscles or being very tired. That particular area may be hurting because of the pelvic area stretching to accommodate the growing uterus and preparing for childbirth.
It's natural for this late in pregnancy to have sore muscles and aches. Being tired is just how you know your body is doing a lot of work making that baby. If it's really bothering you try a nice hot bath! (Not too hot) or have your partner rub the sore areas. Good luck momma