Is this labor?

I'm 38+3 today. I've been having a ton of Braxton hicks and period like cramps in the past week. Just today, the cramps have gotten a lot worse and my lower back is absolutely killing me!! I was in the hospital a week or so ago with contractions that were 3-5 minutes apart but they weren't dilating me so they sent him home. I'm wondering if this could be the start of labor and of it is, when should I go to the hospital???