Constipation in 3rd trimester

Okay people, I'm 29 weeks today. I've never dealt with constipation before in my early pregnancy. As the pregnancy progresses, I think it's gonna get worse.

I have gestational diabetes, so eating prunes or drinking prune juice comes out of the table. I'm eating salad every day and I drink like 2-3L water a day, so the fiber and liquid intake should be fine. The only thing that helped me before was a coffee, actually I drink it every 2nd day. But it doesn't help much now...

I'm open for any suggestions. Thanks!