H.,
I don't know how much my experience will help, but here it is:
My mother was dg'd with Hypothyroidism when she was in her early 20's. There is a 25% chance of passing it to your kids, and she had 4 kids, so we've all been sure to keep ours checked out. Well, guess who got it?!
At around 16 weeks when I was pg with my first daughter I was not gaining weight, was sometimes shaky and lightheaded, nauseous when hungry or too full, and had some heart palpitations. We ran blood tests and found out I had gestational hypERthyroidism. We didn't treat it, other than just avoiding caffeine and eating as much nutritious food as I wanted to, any time I felt at all hungry. That cured the "morning" sickness and shakes/light headedness. When I still wasn't gaining enough weight near the end my midwife "prescribed" a milkshake a day! I felt pretty good through my pregnancy, and the problem went away after delivery. I kept getting it checked when I went to the doc.
I was fine until a few months after delivering daughter #3 (6 years later). I thought I might have postpartum depression. Turns out I had a completely non-functioning thyroid. (After my 6 week postpartum blood work came up clean.) I got on Armour Thyroid (dessicated pig thyroid, not synthroid)and had a huge turn around in my life. I'm basically a new woman now that I'm on Thyroid and Iron (which was ridiculously low - I had zero iron stores). I'm a huge "alternative" medicine supporter, meaning feed the body good nutrition, then use the least invasive/hurtful process possible to cure, but I'm very thankful for the modern medicine we do have when a part of the body malfunctions completely. Hopefully your health will be restored after the little one is not on your life-support anymore!
Blessings on your pregnancy!
js
P.S. From my research, it is more dangerous to have untreated hypothyroid during pregnancy than to treat the it, so don't fret about meds during pregnancy if you need them. You have to have proper organ function (controlled by the thyroid) in order to have a healthy pregnancy and healthy baby.