3 hours of contractions then nothing??

I'm 39 weeks. Last night I went out to dinner and the whole time I was having slightly painful contractions. Like period cramps and they started in my lower back, so it definitely felt different than my normal Braxton hicks. I started timing them and they were coming 3-5 minutes apart. I went home, went for a walk and had them the whole entire walk. Even more painful but still 3-5 minutes apart. Came home and sat down. They continued for another hour or so then just tapered off. What the???? I don't believe I was dehydrated because I drink insane amounts of water every day. I'm a FTM so I have no idea what to expect. I really thought that it might be the start of something and then it just slowed down. I've had some contractions today but nothing consistent or really painful and I lost some of my mucus plug. Is this just my body getting ready? Anyone experience this and go into labor soon after? I'm so disappointed ☹️