TSH + Levothyroxine

I've started 25mcg for my TSH, which prior to Pregnancy ranged from 2.3 - 5.6... so high end to elevated outside normal. I'm 4+4 days pregnant now and been taking it for 4 days. Doctor wants it between 1-2. I'm worried it won't lower quick enough and could cause problems. Anyone have experience with this? How long for it to lower? All other tests are normal (normal T4).