Help!

For the past few days I have been experiencing a lot of cramps it gets worse when I move certain ways and its been hurting on my left side for a few hours nowi would almost describe it as like a period cramp! I am 21 weeks pregnant Im a waitress and I'm on my feet a lot working pretty hard I was doing some research about abdomal cramps and it said some can be serious or it can be harmless I was hoping someone would be able to help calm my nerves a little bit. 
 Thanks!!