Marcia, for most people with hypothyroidism, life goes on as before. Be aware that it takes about
6 weeks for medication changes to show an effect, so we do have to be patient and wait. Also, since the improvement can be subtle because of the slow effect, it can be hard to track sometimes. Doctors will usually follow with a blood test every six weeks or so until you're stable.
In some cases, Hashimoto's thyroiditis is the cause of hypothyroidism, and this can be more complex to treat. It causes the body to produce antibodies to destroy the hormone secreted by the thyroid gland, and frequent fluctuations can occur. We have several active members with Hashi's, and I'm sure they will have more information for you. I've also posted a link to a site with accurate information on thyroid conditions.
Properly treated hypothyroidism doesn't cause other health problems. Thyroid conditions, however, are almost always autoimmune in nature, and it's known that those of us who have one AI condition are much more likely to have others. That doesn't mean it's inevitable, but the chance is there.
Synthroid has few actual side effects, however too much or too little can cause symptoms. The second link posted below discusses this. It's also a fairly inexpensive medication, fortunately.
The important thing is really not to think of yourself as "sick." You have a hormone deficiency which is often easily treated. Please let us know how things go for you.http://www.mayoclinic.com/health/hypothyroidism/DS00353