Hypothyroidism

Hello, I am not a thyroid cancer patient, in 2009 I had stage 3 laryngeal cancer. Had chemo and radiation to the head and neck area. Earlier this year I got badly constipated and suffered great fatigue and achy feelings in my legs. My doctor tested my thyroid and it was showing hypothyroidism, I was told after the radiation that this may happen but did not know the symptoms. My doctor started me off on a low dose of levothyroxine and gradually increased it to 100mcg. A follow up blood test showed that my thyroid reading was now 0.35. he had me stop for a week then go back to the 50mcg. Follow up test showed up at 5.3 went to 75mcg. Point is, I still feel lousy, fatigue still, muscle aches and constipation, I also put on 10lbs seemimgly overnight. I am taking the medicine every morning at 5 am,I then get up at 6:30 and have my breakfast. I have not been taking the pill with 8 ounces of water, just popping it in and downing it with a mouthful of water. I have milk with my cereal and this of course has calcium in it. I only heard about these things today by going over some posts here. Any advice on how I can get to feel better, when I was on 100mcg I did feel better, still constipated but better. Thanks, Denis