Why am I losing weight so fast?!?

Last year at the beginin of the summer I weighed 225 and was about 5'8..*im 18 years old btw* and during the summer I diet and excercised daily and by th eend of July I weighed 185 I went for my yearly physical in january and I weighed 160 and now it's march and I weigh 137 the doctor told me the only thing wrong with me was I had a vitamin D defficiancy and an overactive thyroid and I have also grown an inch-3 inches could anybody please take this paranoia away from me?