Cramping after Doppler

I had my 12 week check up today and we used the fetal Doppler for literally about two minutes and found the heartbeat really quickly. I have had a transvaginal ultrasound before with no discomfort afterwards. About an hour or two after my appointment I have been mildly cramping. I googled cramping after Doppler and a lot of woman experience but this but no one knows why. Has any other ladies experienced this?