Many doctors are not clued up about hypothyroidism I am afraid.
Most adults start on 50mcg levothyroxine. The starting dose of 25 mcg you were given is much too low for most cases and ought to be increased by 25mcg to 50mcg, as being left on too low a dose can actually make you feel worse eventually.
Please go back and ask for an increase to 50mcg, which is still only a starting dose.
After 4 or 5 weeks on 50mcg your doctor should be considering your response, by blood test if necessary, then increasing the dose as necessary.
He will probably be monitoring your progress by the TSH like most doctors, about which only a blood test can give him information so he should have told you to come back in roughly 4- 5 weeks, it varies, so that he can gauge your progress usually by a further blood test. When you have reached a suitable dose you should lose the extra weight without even trying, as the extra weight is because the hypothyroidism has lowered your metabolic rate.
You will really need to start learning about hypothyroidism and its treatment even if only in self-protection. Please consider going to thyroiduk.org
They have a wide range of very helpful informative sheets available on their website. I strongly advise you to read them as it does seem that your doctor is rather clueless, just as mine was.
It would be so useful if you could post on here your blood test results, as well as the reference ranges, important to quote them also as labs use different ref ranges.
I do hope that things go well for you. Start by learning as much as you can.