early labor ?

Haydin
I am 33 weeks and 4 days 
This morning I went to the bathroom and when I wiped I'm pretty sure I lost part of my mucus plug. Just a clear-ish yellow color. No blood or anything like that. But now I am having really bad lower back pain. It lasts several minutes then sorta goes away and then comes right back. 
I had a CS with my first and never felt any of this. I never even had Braxton Hicks last time. So that could be what this is but it's making me nervous