OP that sounds awful for all of you. Without wanting to get all TMI about the constipation, if she is feeling the urge to go but nothing comes down the pipe, as it were, ask the pharmacist about suppositories.
Definitely keep pushing the GP for blood test. On reading your OP I thought PCOS or thyroid. But I am not a doctor, nor do I play one on TV.
GPs can be twats at blaming everything on an existing diagnosis. I have a family member who has been having increasingly severe symptoms of tiredness, digestive problems, joint and muscle fatigue and brain fog.
She was basically told "It's all due to your anxiety and depression so fuck off "
After 6 months or so trying to get someone to take it seriously, her BF paid for a private consultation with a specialist in Chronic Fatigue Syndrome. Turns out she doesn't just have CFS but also hypermobility which has led to Fibromyalgia. She also has IBS.
The specialist wrote a quite sharp letter to her GP. It has been incredibly life-limiting but she is slowly recovering more energy. I'm so angry on her behalf that it took so long, and going private, to get some actual fucking treatment.