I think it could be the start of contractions, but really you'll just have to wait and see what happens. I wouldn't be concerned about it.
I agree with this. With my first pregnancy I never had any BH, didn't lose my mucus plug (or didn't notice it) and didn't have a bloody show, went into labor at 41 weeks 6 days and what you're describing sounds like what my early contractions felt like, but only time will tell. GL!