I'm really concerned about them not giving you a stitch, and their excuse that IF your waters break, it will be hard to deliver. I had PPROM with baby #4, which was a total fluke... but many many MANY women with PPROM have their waters break because of incompetent cervix. Did they check your cervical length any of those times??? The fact that this has happened more than once to you really scares me. If you do have IC, a stitch can help you SOOOO much and there's a better chance your waters won't break again.
Quite a lot of PPROM women also have clotting disorders. They haven't been able to diagnose me with one, either, but they still put me on the injections. The reason is because suddenly during a couple year timespan I ended up being hospitalized 3x with blood clots in my lungs (not like it had ANYTHING to do with being 30, smoking, and being on BC pills). So even though I have been tested for everything under the sun and it's all been negative, they feel that I'm very sensitive to estrogen, and I could clot again very easily whenever pregnant. They won't even consider doing aspirin for me since I really dodged death 3x.