I'm sorry you slipped up yesterday. I hope that you are feeling alright today. The first thing I would say is be kind to yourself. Don't beat yourself up about the slips; that's a sure way to making more. Just try to relax about it and take a deep breathe or 10 deep breathes and stay in the moment. It's not the end of the world. We live life a moment at a time.
As for sticking to the diet, I don't think there is any trick. I have found I just have to get stubborn and not allow myself to be taken off track. I am the one in charge of managing this condition. I keep in mind that I have a choice about how I will feel both emotionally and physically. I can have the pleasure of the gluteny treat now and feel awful later ie abdominal bloating, cramping, gas, diahreoia, brain fog, insomnia, heart palpitations, anemia, or I can find something else to eat that gives me pleasure and continue to feel good. With your family, it may take some time, but I think if you take the lead and treat this seriously they will eventually come around. Let them think you've gone off the deep end. It really is none of their business. It's your body, your health, your choice.
I understand, it's not easy to do sometimes. Try not to panic. It will pass.
Have you had your thyroid tested? How is your standard blood work?
Do you sleep long hours and wake up still feeling tired? Hair falling out and coldness and lack of energy can be related to hypothyroidism.