If it gets to the day of the interview and you're having a bad time with your endometriosis I would ring the person that is meant to be interviewing you and ask to reschedule. If they are understanding, they will reschedule. If not, then it's not the right job for you. Being willing, open and honest will always serve you well. In terms of the doctors, keep pushing it and demand that they do something about it and state that it is really affecting your life. There's loads they can do if you have endometriosis, even putting you on the mini pill might be able to help! Exercise can also help with pain management.
You will get there I promise, you have your whole life ahead of you. I'm nearly 26 and there are loads of people my age still trying to figure out what they want to do with their life! At the end of the day though, health comes first and I would definitely push the doctors more. Not getting your endometriosis under control will only make working harder for you.