When were both tests (or how soon after baby and how soon after sertaline)?
To me (and probably GP if he saw results) it looks like tsh is resolving and moving in the right direction. At the same time you were right to look into it imo due to family history.
(Healthy) Thyroids naturally grow and change during pregnancy. Postnatal you can be a time when hypothyroidism kicks in. As you are post baby, there could possibly be something going on, at the same time thyroid could be adjusting. I'm not a doctor and I don't know what is expected post baby.
It's worth being aware of it runs in your family. This could mean eventually something could go wrong, but also possibly not yet. So, it's not unreasonable to ask for another test in the future esp if symptoms get worse. (I would sort of bet you might eventually. However my sister isn't hypo, I am and my mum is.)
The problem is its a very slow process and clinically your tsh is improving (t4 and t3 are a bit low but these vary and are not as static as tsh) - this improvement is good.
Now - sertaline is a tricky one. If you were taking thyroxine, you might need a little more. Bizarrely it does affect it some how but the info I have is regarding if you have hypothyroidism and are on thyroxine. (BMA thyroid book, can get from Amazon, it's a very good reference guide and BMA approved.
However I have no idea what that means in regards to normal thyroid function and sertraline. It's completely possible it's slightly impacted but thyroid is readjusting - this is total speculation on my part.
Tsh is released to stimulate the thyroid to make more t4 and t3 but this can be a very slow process hence why tests can be 3-6 months of being monitored.
I know this is probably frustrating, but as I say it's not unreasonable to keep an eye on it in the future due to family history.
If tsh gets to around the 4 mark GP will consider treatment, and certainly antibodies.
I would definitely get your ferritin much, much higher - eg over 70. Take with vit c or orange juice. And check your b12 and vit d are optimal too.
(Regarding antibodies - I know I had a different one to the usual one so I don't understand that process now) .