Preterm labour

I’m 29 weeks pregnant and I’m in the process of moving. I donated some boxes of books to value village and while I was lifting the boxes (I know I shouldn’t have) I started getting what I think was Braxton Hicks. I didn’t think much of it because I know it’s common but I made a mental note to not lift anymore. Anyway, so I’m in the car driving home and my tummy is feeling tight and then I get sharp vaginal cramps. It’s been about 10 minutes and no more cramps.

Is this just a symptom of Braxton Hicks or could this possibly be the beginning for labour?