Thigh pain and heaviness

So I'm 36+5 weeks and today I have been getting a slight pain and heaviness feeling in my inner thigh's and my belly's been tightening like crazy when I walk. I walked to the mail box (only like a 10 minute walk to there and back) and it felt like my legs weighed a ton and my right thigh kept getting a slight pain in it. I didn't feel like this yesterday.. I Aldo think I lost my mucus plug this morning but I'm not sure.. Could this be an early onset for labor?