Muscle cramp in side of back?!

Catherine • Hi! I'm Catherine, I'm 29 & mummy to 3 little boys. Mason Elliott 26/03/16 💙 Ezra George 22/05/18 💚 Archie Emerson 02/07/20 💛
Im 18 weeks pregnant and I woke up last night with an excruciating pain in the right side of my back? It made me feel really sick and I almost fainted it hurt so much. I called the doctor and she said most likely nothing to worry about and to put some heat pads on it. 
Have any of you ladies had an experience with this as its kinda scared me :/ 
Thankyou!