It’s so hard being invalidated

For background info, I am 16 with diagnosed chronic pains and undiagnosed ocd. My older sister is 18, in college, and works a job but still lives at home. We have two bathrooms. Because of my ocd I can’t bring myself to use one of the bathrooms and it has nothing to do with cleanliness. I had just been out to an amusement park for 12 hours, it was very hard on my chronic pain and very overstimulating. I got home around 1 am only to find out my sister was using the bathroom that I use. Now this isn’t a problem, just because I have a compulsion doesn’t mean I own that bathroom. However at 1 am she decided to take a very long bath. Not a shower. Not a quick bath either, the type where you pamper yourself. I was willing to wait, I waited ten minutes then fifteen minutes, then twenty. I don’t know how long she was in the bath for before I got home but all I asked was for her to hurry it up. But of course she blew up. Again I was very overstimulated and blew up too. Apparently because i went to an amusement park and had fun my pain doesn’t compare to her fatigue from work and school. I’m in high school but I take college courses. I don’t have a job but I shouldn’t need a job to be stressed. After some very angry arguments we I did my business and went to my bedroom. Everything just collapsed and I had a mental breakdown. I don’t think my family actually understands how much physical and mental suffering I go through. My mom said “we needed to talk tomorrow”, but only to me. She clearly favored my older sister in the argument and now I just can’t stop crying and finally go to bed