My Daughter Is 23, She Has Many Symptoms Including Weight

My daughter is 23, she has many symptoms including weight gain that she can't lose even though she's a runner and doesn't eat that much, she is very lacking in energy, she gets canker sores frequently, she's cold and has some digestive/ stomach issues. She has had a physical and a basic thyroid test which was normal. I feel she has thyroid or endocrine issues, but I can't get her into a doctor that specializes in this without a referral from her doctor who will not because he thinks she's fine. What can I do to get her some help?