Braxton Hicks or round ligament pain?

First pregnancy. And I’ve been having this tight pain on the left side of my stomach, for over 8 hours now. Comes and goes every 5-10 minutes and it hurts so bad i feel like i need to cry, scream out in pain and stop what I’m doing. I had to leave work because of it. Should i be concerned? Go to the ER? Just rest? Is it contractions or round ligament pain?