Twin mamas- when did you start slowing down in pregnancy?

I’m 21 weeks and these last few days I’ve noticed a drop in my physical ability to get out of bed and just getting tired very easily from standing or walking. Any tips or recommendations on how to keep physical energy up? I still have a while to go and feel a bit down that I’m slowing down already. I haven’t been working out or anything n (I have a toddler at home which I consider exhausting enough)