like babydust said Physlium Husk is a good fix but you should really look at your prenatal. Lots of women take a single easy 1 pill prenatal and they usually combine the iron with the calcium in that 1 pill. Not good at all. Iron binds with calcium, dairy products and will constipate the heck out of most of us.
My colleague at work was doubled over with gas & constipation until she got the liquid iron - she was taking an all-in-one before her doctor switched her to pregvit (see below). Then when taken with a little orange juice seemed to sail fine through her pregnancy without all that pain.
50% of time it's the cheapie iron they put into the all-in-one prenatals, 50% of time it's diet related. You sound like you eat lots of greens so yours is likely pill related. When the carb & meat on your plate takes much more room than the veggie, you're in for trouble. Meat, veggie & fruits are great for keeping things going, bread/rice/pasta etc will slow things down, rice is a great fix for diarrhea! The more carb, the more constipation.
Try getting an easily absorption iron like this:
https://www.florahealth.com/product_categories.cfm?category_id=4&prod_id=87
https://www.aor.ca/products-page/advanced/ortho-iron-4/
and make sure your prenatal doesn't combine calcium with iron. Here's one that splits them iron in the morning, calcium at night:
https://duchesnay.com/en/pregvit