Odd pains. 15 weeks pregnant.

Me and DH were at the grocery store earlier and I started feeling a lot of pressure very very low. I went to the bathroom scared that I was going to find blood but nothing. I felt a little better after urinating but about 5 minutes later it his me again and even harder. I tell my DH we have to leave because it was so uncomfortable. We head to the check and are waitin in a long line. I decided to walk around a bit while waiting on the line. I head back to the checkouts and suddenly get a sharp pain high on my sides, both sides. It almost felt like someone poke me with their fingers on both sides at once. A few steps later it hits again and the pressure is horrible. I get the keys from my husband and wait in the car. It goes away almost immediately after sitting down. That was hours ago and I havent had problems since. Any ideas what it was? First pregnancy....so I have no clue.