So you will have your blood test done again in 4 weeks as it takes a while for thyroxine to take effect, to see if dose needs to be changed. The policy here during pregnancy is to test 4 weeks after a change in dose then every 6/8 weeks after that, once your levels are stable (ie your dose is adequate), throughout pregnancy. it helps to coordinate your thyroid blood tests with your antenatal blood tests if you can, as they can at least do it all at the same time then and means fewer needles for you!
Do you think you might have had some symptoms of hypothyroidism before the blood test picked it up?
Here it is usual to have consultant-led care if you have thyroid disorder, although hospital have agreed to me being looked after by GP as all they do is monitor blood tests, which my GP does anyway. I wouldnt get any extra scans though.
btw, TSH is a hormone which basically gets released to send a message to your body telling it to produce more thyroid hormone, so generally speaking a high TSH level means that your body needs more thyroid hormone than it currently has in the bloodstream (there are additional things they look at too, eg T3, T4). There are guidelines on what the TSH should be at each stage of pregnancy, which your GP or consultant should monitor and adjust dose accordingly.
FYI I was actually diagnosed after I had DC1, although I had probably been borderline hypo for ages as it rubs in the family. You can get s condition called postpartum thyroiditis, which means your thyroid hormone levels can change quite a bit and you can often be hyperthyroid a few months after birth, then swing the other way to hypothyroidism.
Obv don't know if you will continue to need thyroxine replacement after pregnancy but if you do, (a) all your prescriptions will be free and (b) if you get pregnant again see your GP asap, as you need to increase your thyroxine dose by about 30% straightaway as you need more of it..
Um, hope that helps but feel free to PM me if you have any questions :)