How to gain energy?

I’m a pregnant mom with a toddler and I am so exhausted. I take my prenatals everyday, I drink 80-100 oz of water everyday, I exercise the best I can with my son, I eat healthy and I nap when my son naps. I still have no energy. It’s becoming so hard to sit up on the couch some days. I feel so awful for my very active son.

What can I do to get my energy back up? Anything I can take?

*yes I’ve asked my doctor and all he said was sleep should help. I go again in three weeks but i can’t spend three weeks this drained and not physically being able to keep my son occupied.