pain on the left of my lower abdomen

I'm 20 weeks & 5days pregnant and I'm having a pain on my left lower abdomen but the pain doesn't come ago. It only cause the pain when I get up in bed, when I put on some clothes and lift my legs up, when I sit down and when I roll over in bed. I don't think is round ligament pain because that pain it comes and goes in a minute. I been having this pain 2 days now.