Welcome back to Healing Well. I am wondering if you have ever been in any kind of therapy. You wrote your racking your brain to figure out why this is happening. May I suggest you work on dealing with how to get through the attacks or learn to prevent them. None of us know why they happen to us and not other people.
It appears you are under a lot of stress without much for a support system which is most likely contributing to the increase in anxiety. Have you tried journaling? Writing your thoughts and feelings down is very helpful. Include what you were doing when the panic attack started.
Also CBT therapy is wonderful. If you cannot afford it here is the link to the online site. Moodgym is a free self help program to teach cognitive behaviour therapy skills to people vulnerable to depression and anxiety.