Miralax doesn't work for me...

Lucia
I'm so constipated I want to cry! This just started a couple of weeks ago (I'm almost 30 weeks pregnant) and because Im taking iron supplements, it's getting worse.
Doctor told me to drink Miralax but really, that product it's a joke for my body. Don't know what to do. Just send my hubby to the supermarket to buy me some dry prunes and see what happens. Feels like I'm not gonna be able to poo... And I dont want to push harder because Im afraid of hemorrhoids. 
What else can I take for this constipation?
*The problem is not that I dont have a bowel movement... I have the urge to go, it's just too hard to push... You know what I mean, right? And It hurts very much.