I agree with a2stylist, seek a second opinion, third or fourth and don't stop until you feel like you are getting somewhere. I was miss diagnosed so many times before they finally figured out it was endo, and I wonder if we had found out earlier would things be different... best of luck hun.
Find a new Dr. You are NOT too young. I had my first diagnostic lap at age15 for Endo. Since then I have had too many to count.( I am now 35) But I did end up having two beautiful children in those years. You just need to find a good dr who is skilled in treating Endo.(if that is indeed what it is) however the only way to really know if it's endo is through diagnostic laparoscopy.
I am 23 as well and suffere the same symptoms including painful intercourse. I finally found a doctor who believed me, we did a diagnostic laproscopy and she found endo on 1 ovary and 1 other place. I hVe suffered from severe periods since I was 11 and been on the pill since. This included constant vomiting, inability to walk and drive due to pain.
I had serious complications with the laproscopy leading to a bowel resection, ileostomy placement and ileostomy reversal.
My advice, demand an ultrasound, if it shows up clear and you're willing to pay, or insurance is demand a laproscopy. 21 is not too young to suffer from endo