Is is safe?

I was very constipated since the beginning of my pregnancy but then it got better. I was so happy since it's so uncomfortable. Now I back to being constipated. I have been taking fiber and stool softeners but haven't had the urge to go in about a week. I have tried prunes, fiber, miralax and stool softners all of which I don't find relief in. Milk of magnesia seems to help and I was told it was safe. My question is it safe to take once a week?