Are hemorrhoids dangerous?

Since i had my son in April 2017 I’ve had a hemorrhoid, it didn’t bother me much only sometimes and now I’m wondering if that’s why I’ve been having issues with constipation and gas? I’m pregnant again and have had several pelvic exams wouldn’t my doctor had said something if it looked severe? Can they be dangerous? It hasn’t caused many problems other then that if that’s what the cause is, but since being pregnant again it’s bled a couple times from wiping.