My wife was sent to an endocrinologist but it was already known she had hormonal issues. Below is what I posted on another topic on PCOS. It might help explain.
My wife has PCOS with insulin resistance - also called metabolic syndrome sometimes. The guest post above explains it pretty much the way it was explained to me. We already knew she had hormone issues due to hypothyroidism. Despite treatment, she still couldn't lose weight. She also has a long history of very irregular periods and some hair growth (actually not that uncommon without PCOS as I understand it). We went to the gyno and PCOS was the diagnosis (she already had the blood work results from our family doctor). She was prescribed metformin and sent to an endocrinologist to determine hormone treatment.
As stated in the guest post above, as I currently understand it, one hormone imbalance causes another hormone imbalance. This continues full circle back to the first, each feeding the imbalance in the other. Despite what you might expect - it surprised us - too much testosterone in a female does not generally lead to a higher sex drive, although it can and is sometimes prescribed for this purpose. In men, testosterone has a direct impact on weight loss. As explained to us, this is not what happens to women, they gain weight instead!
We were told PCOS is one of the greatest misdiagnoses for women. Often nothing is checked beyond the thyroid and estrogen, the conventional culprits of hormonal weight gain. The assumption, again as explained by the doctor, is that if these are being treated then hormones are not the issue - meaning you supposedly eat too much - and they may very well be wrong.
I don't know how a diagnosis was made without blood work or other tests. But unless you already have reservations about your doctor's competence, I trust she knows what she is doing. Nonetheless, a second opinion is not going to hurt and your doctor should understand this and may very well promote the idea.
As to the effectiveness of treatment, we haven't been on it long enough to know for sure. When seeing other medical professionals, you will get asked if you have a diabetes and they may not believe you if you tell them you don't. They often assume metformin means you have it. You may or may not have diabetes, but metformin alone does not make it definite. This is where we were advised to mention metabolic syndrome.
Please note that I am not a doctor and very well may be wrong when discussing medical issues. Please let me know if you have corrections to my understanding. As always, follow the advice of a doctor who you trust over anyone else.