What happened!?!

So today my husband and I went to Lowe’s to get new plants and bushes for this year and then we went to Kroger to grocery shop. I was fine at Lowe’s. As we were walking into Kroger I had this pain that stopped me dead in my tracks. It felt what I can only figure to compare to as a charlie horse and it was in my lower back, my lower belly and it went down my legs. It lasted several seconds but it was the craziest feeling. I stood still to see if anything else would happen, nothing. Walking through and finishing our shopping trip I kept having the feeling it was about to “cramp” again. It has yet to actually happen again and it’s been about 3 hours. Does anyone know what that feeling was? Or has it happened to anyone? I’ll be 36 weeks Sunday.