Sorry for the delay, just saw your post when I signed on this morning.
Thyroid hormone (your own or synthetic) works to regulate metabolism in every cell in your body. This means the hormone controls the conversion of oxygen and calories to energy so that your cells can use it. This conversion is "metabolism".
Without this conversion, your cells cannot use the oxygen and calories. So, with the calories running around with nothing to do---your body will store them as fat. Not to mention that your cells cannot do whatever their particular job is---this is what causes the symptoms of hypothyroidism.
Thyroid medication does not cause weight gain. There most likely are other things going on that could cause this. Most likely scenario (at least for most people): to gain 14 lbs in 3 months you would have to eat 540 calories more per day than the body needs. That isn't very much (a little here, a little there). We very often just do not pay attention to how many calories we ingest.
The endocrine system is very complex. If your doctor feels you are getting too much thyroid hormone based on test results and symptoms you have (too much would cause palpitations, poor sleeping, jitters, etc), then he would reduce the dose.
Many people put too much emphasis on weight loss and gain when taking a thyroid supplement. Usually, for someone with mild hypothyroidism, which yours may have been, based on your TSH, any weight gain is caused by fluid retention. This fluid retention is lost when you start taking thyroid, so you get some initial weight loss. More severe hypothyroidism, or milder forms left untreated, over time will cause actual fat weight gain because the body cannot use the calories ingested for energy (so you have symptoms of fatigue, sleeping a lot, weight gain without much food intake, etc).
Here is a link that explains thyroid function, and some of the complexities of diagnosing what the actual problem is and treating it: How Your Thyroid Works. There are also links on this page for more information about thyroid problems, tests, treatment.
Whatever you decide, you should discuss with your doctor. Perhaps you do not really have hypothyroidism. Your problem might be something else. A TSH of 4.5 is a high normal, or slightly higher than normal (depending on your own labs ranges, of course)
It is very natural for older people to gain weight in the 5th and 6th decades of life. This is a time when everything starts to slow down, and we often don't use up as much energy as we used to. Exercise and controlling your diet are the first steps to helping yourself. And exercise is the best way to boost energy levels.
So, while you are working with your doctor, take a serious look at your diet. Keep a food diary to see where you can make some healthy changes. Also, if you are continuing to take thyroid hormone, make sure to take it first thing in the morning on an empty stomach about an hour before eating. And do not take any calcium containing foods or supplements for 2 to 3 hours afterward, as calcium can block absorption of the thyroid.