Upper Ab Pain at 21 weeks

Tausha

In the last few days, I've noticed some pain my my upper abdomen. Just now, i was laying on my left side for a while and it started burning right down the middle of my abs. It started to make me nauseous. After sitting up for a few minutes, it's a lot better. Is this what diastasis recti feels like?? Or any other ideas what might cause this kind of pain?