Postpartum depression feeling like bipolar disorder but moods changing daily, and really bad when on period?

I'm already on antidepressant since before I was pregnant. This is my third baby and have never noticed it this bas before. I always had anxiety and irritability around my periods but after this baby ( she's 4 mo) it seems out if control. Had my blood work done, everything normal. I feel as though I'm losing my mind sometimes and ok the next, but when my period comes I have noticed its like I'm totally a different person. I just hope this goes away.