Third trimester constipation

So long story short pre-pregnancy I had IBS-C and already struggled with constipation. It’s been terrible all throughout pregnancy but since I hit third trimester it’s a million times worse! I’ve already been in talks with my OB about it. She suggested miralax a few months ago which sometimes helped, and milk of magnesia when it’s really bad. I already drink a ton of water and make sure im getting fibre but I think it stems from an internal pelvic floor issues (im working with a PT, and we are going to address this post pregnancy). Any other tips and tricks to help me “go” would be lovely! Even if I do take milk of magnesia I go the next morning and can be constipated again by the next day. I also have a squatty potty which helps a bit!

Ive tried coffee but it keeps giving me heart palpitations now so I’ve stopped drinking it.