Labor or not ? Someone please help me out

Ok so it's my 3 rd pregnancy , lost my muscua plug just now and I am already one  CM dilated but hVe been doing a lot lately an I'm 38 weeks , do I have to have contractions to be in labor ? My other 2 pregnancies were different and my lower back is really hurting . Does that mean I'm  not in labor because I'm not contracting but I have back pain . How would I know? Does it mean since my muscua plug is gone that I'll go into labor ?