Coconut oil works well for me, better than any of the OTC hemmie cream.
Sitting on a narrow ice pack also works really well. If it weirds you out to have your undies pushed right up in there just change into clean ones when you're done.
I had some leftover herbs from a birth (the mix that midwives will give for a sitz bath) and made a strong tea with that, did a sitz bath with part of it and soaked some cotton balls with some of it. Put the cotton balls in the freezer and sit on one (place it right on the hemmie) when needed. Very cold but works well. I sit on a folded prefold when I do this as it will melt into a puddle.
There are also some homeopathics out there that can help. I have no knowledge of safety during pregnancy, but I feel safe enough taking them.
Something that is supposed to help with either diarrhea or constipation is psyllium husk powder (same as the ingredient in Metamucil). I have many gut issues but I tend more toward the loose stool end of the spectrum, but I've heard from many others that it helps with being stopped up as well.
If you decide to try psyllium, start very slowly, with like 1/4 of a tsp and let your system get used to it before upping the dose. If you take a whole dose right from the start it can cause gas. I take it every day.