First of all well done for overcoming life's challenges and barriers that are put in front of and getting over the hurdles it throws up. It took me financially 6 years to do the same with my own situation.
Any how; if you have your old study material available, re-read that core material and don't merely concentrate on one set of materials or you might become biased, which may lead you astray. Cybrary the online community is a good source of materials, with different instructors, which may give you a different context, which may help.
Give yourself some space, to chill out between sessions, to ensure you absorb the material, before you challenges yourself again. Note down the weak areas, and put some more effort into resolving any difficulties. If you are having difficulties with the material especially the core fundamentals, find a different source, to provide a different context and angle, which may unblock any barriers to your learning.
Have multiple examination sources, some of the examinations solution providers from the UK, for instance, have some good material and a different set of questions to stretch you, so you don't become heavily dependent on the materials in front, but that you think around the subject..
It is challenging, but with your experience, look for the core issues, and ensure they are strong and that you can apply them to any situation you encounter.
Not sure this will help you - but being frustrated, may actually raise barriers and perhaps you need give yourself some breathing space, even if you think this is very hard to achieve, given what is going around you.
Find some space, for a few hours and do something different - walk, drive to your favourite place early in the morning for instance and then come back refreshed. Some deep breathing techniques from Yoga may help as well.
