Low ferritin and vitamin D, just started supplementing. How long does it take to feel better?

I’m 27 weeks pregnant and at my last OB we did labs and they came back with low vitamin D (14, normal range 30-100) and low ferritin (11, normal range 15-150). I’m starting prescription ferrous sul for iron deficiency, and they recommend taking 2000 IU of vitamin D per day. I’ve been so beyond exhausted lately and I’m certain it’s due to this. The only thing I can make myself do physically right now is go to work. I have nothing left to give beyond the bare minimum. I’ve had iron infusions prior to pregnancy when my ferritin level was lower than it is now, but I’m not sure how much the vitamin D deficiency is playing a role in how I feel vs the low ferritin. Has anyone else had this problem? How long did it take you to see improvement after beginning supplements? Thanks!