I had my thyroid "destroyed" 20 yrs ago with the radioactive iodine treatment for Hyperthyroidism. Now I take daily thyroid replacement to make up for what my thyroid can't make on it's own.
When you are in the first year of treatment, it really is a balancing act with finding the correct dosage of hormone for you and that can only be determined by looking at the results of the blood tests. Now, I get checked annually, or if I have lost/gained a significant amount of weight.
There are symptoms to watch for, as well, to indicate if your thyroid is running low/high. Consult your doctor and learn the symptoms to watch for. Also, know that any regular exercise and healthy nutrition is always good for a person. You will feel better, even if the weight doesn't automatically drop back off. I asked my doctor, once I was within the "normal" limits according to my bloodtest, if there were any limitations re: diet and exercise and he said just eat a healthy diet. I have noticed on medication literature that soy products are known to limit the efficacy of the hormone medication. So, ask the pharmacist if/when soy products can be eaten to avoid a problem. I changed taking my med at bedtime because I enjoy a soymilk smoothie for breakfast a couple of times per week.
Sorry this is so long, but I've been through it and just thought the info would help.
Take care of yourself.