This Story of You is wonderfully done, filled with question-raising bits (like the letters to a prisoner). I get a real sense of your travels and how flash fiction may fit in. Since flash fiction provides a lot of practice in real storytelling, your goals are in reach.
One thing that has been important to me as I’ve grown older is finding what times are best for me to compose something new, edit a draft, etc. It isn’t the same for everyone, so it may mean testing 15 minute tasks at different times of the day. This might be especially good for you since you’ve lost your “go-to” writing time. It takes some patience to do this, but it is likely to reduce frustration (and make writing more fun).