I'm 39 weeks, and lost my mucus plug with slight cramps. and i'm extremely tired, could this be labor?

Labor?: I'll assume that this is your first pregnancy. Towards end of pregnancy, when your cervix begins to dilate, you can see a lot of mucus discharge. This is not labor. It maybe 2-3 more weeks before labor begins (going beyond 42 weeks is not safe). You will know when you are in labor. Labor contractions last 40-60 seconds and are quite strong. When they are every 4 minutes and don't stop, = labor.