Well, the majority of the problem is that my ex didn't work, so my income married was the same as my income as head of household. I was in a lower tax bracket married with my income than I am HOH with that same income. Additionally, I didn't have ex's medical expenses to use as deductions. I am only allowed to claim 2 of my 3 children as dependents per the divorce settlement (he wanted one so he could be HOH too). But I make too much to get a credit for them anyway.
My childcare expenses were all over the place last year. There were no reportable expenses (different caregivers, all under the table, etc...). Not the best way, but the reality at the time.
And, because of the money issues, I couldn't afford my own medical treatments, so I skipped them. That left me with fewer medical expenses to deduct as well...
Anyway, it just snowballed. We'll see what happens!