Sounds like round ligament pain to me.
Trust me, if you pulled a muscle in that area, you'd have a hard time standing upright.
Your joints are soft, which means that your pelvis can shift in and out of position quite easily. So you can feel pain in your actual crotch (feels like a burning pain) from time to time.
Otherwise, you'll feel round ligament pain, which is just a normal part of stress and strain on your growing belly. Feels like a really sore muscle. Take a rest, or actually lift your belly up with your hands, and it should go away fairly quickly. It'll come and go.