than what doctor can help me find out if i have endometriosis
The Gastroenterologist will view your colon but won't be able to diagnose endometriosis.
I've never heard of anyone being too young to have this! Keep your appt. with the gastro doc because he can rule out any intestinal problems and then see an OB-GYN but not this same one. How did they determine that a cyst ruptured and not your ovary? I think you are correct to keep pushing for answers but try to maintain your composure so you can have a conversation about what is happening with the doctors.
Don't hesitate to ask any, and all questions and don't leave until you have a full understanding of what they think and why! The doctors work for you! I do wish you all the best, and let us know what you find out! Stay proactive with your health, you know your body best! Take care.