Idk what this pain is. 18 weeks pregnant.

Its like a throbbing pain down low on the left side, it will come and go but when it comes its crippling. Like i almost am thinking about calling the midwife or on call nurse or something, it feels like the throbbing is getting worse.

What would a cysts feel lke? Can you have one this far along in pregnancy?

You can have a cyst. I remember having one with my pregnancy with Sophia when I went in for the anatomy scan at around 22-24 weeks.