Hi, wingsfree,
Glad you're feeling so much better!
It can take 3-6 months for an anti D to get fully into your system, so, you could be having break through depression as a result of that fact. Otherwise, I honestly don't know. But, I do know that I have to take care of myself physically, mentally, emotionally and spiritually if I want to feel good -- with or without meds.
Keep up the good work. Keep a journal; you may find it's related to something else - like your monthly friend; or something you've eaten. And keep the faith!
Shalom!