Glad you are feeling more human I also find multivitamins help perk me up a bit.

I have also been feeling absolutely exhausted since I had my boy and, after a sleep study, I found out that I have mild sleep apnoea - just bad enough to disturb my sleep and leave me constantly fatigued. So I spend my most of my days tired and can sleep forever if given the opportunity

So if your bloods are inconclusive, the possibility of sleep disturbance may be something to explore as a cause for your tiredness.

I hope you get to the bottom of it and get some answers.