Postpartum weight loss

So I gained 40 pounds during my pregnancy. I’m almost 4 weeks postpartum and during the first week I lost 20 pounds. I have been at a stall for 3 weeks now - no weight loss whatsoever. Does that mean I gained an extra 20 pounds of fat? I started running at 2 weeks postpartum and began resistance training this week and so far I’ve gained 2 pounds...what’s going on?

By the way I’m exclusively pumping.