I had postpartum thyroid dysfunction after my latest pregnancy (and possibly after one of the others but not diagnosed). It appears to have resolved itself just about now.
In my case I was hyperthyroid and this was only discovered when the GP ordered thyroid function tests to rule out thyroid issues in relation to a cluster of symptoms including arrhythmia, tachycardia, insomnia and anxiety.
As I understand it, PPTD is a flare up of underlying autoimmune disease (other autoimmune can include diabetes, lupus, IBS and rheumatoid arthritis). During pregnancy your immune system is suppressed, but as it comes back to normal postpartum it can do so dysfunctionally, erroneously identifying the thyroid or other organs as foreign and flooding the site with antibodies.
Have you had a thyroid antibody test or just thyroid function? The thyroid antibody test can be cleanly diagnostic for PPTD according to my consultant endocrinologist, for a given set of symptoms including recent-ish childbirth 
although fwiw my symptoms weren't obvious enough to warrant investigation until DC3 was over twelve months old (it's rare to take that long).
Most women find that their thyroid levels correct by themselves over a few months, and regular blood tests are used to monitor progress. Then you have to watch out for the recurrence of symptoms after subsequent pregnancies and in future more generally. I'm still on monthly bloods but should be discharged by the consultant in August and then six-monthly bloods for the rest of my life.
In the meantime it can be necessary to treat some of the symptoms. In my case the heart problems were treated with beta blockers (which also help with anxiety).
No idea about the liver, sorry.