Gas Pains????

I'm 21weeks 4days today and ever since yesterday I've been getting these really bad abdominal pains in my lower stomach. It lasts for a few seconds and then I pass gas. Ive been constipated and I am wondering if that's why? I don't know what Braxton hicks are because I'm a FTM but I'm sure that's how they feel somewhat because it's painful. Just wondering if any of you ladies have had anything similar and if it's normal?