Having an underactive thyroid does not mean you have cancer, it means you are hypothyroid (i.e your thyroid does not produce adequate hormones).
Your doctor should have tested you for Thyroid Stimulating Hormone (TSH), Free T3 (FT3) and Free T4 (FT4), at the very least. It would be good if you had been tested for thyroid antibodies, as well; and yes, an ultra sound would be a good idea to confirm/rule out nodules (nodules do NOT equal cancer).
While tracking your temperature might be helpful in diagnosing hypothyroidism (under active thyroid), you've already been diagnosed, so that probably wouldn't be much help to you.
There are certain supplements that might be helpful; however, if you have Hashimoto's Thyroiditis, which is an autoimmune thyroid disease, in which antibodies attack and eventually destroy the thyroid, iodine is often contraindicated.... which means it can be more harmful than helpful, so I'd steer away from the kelp. In addition, OTC thyroid "helpers" have no actual hormones in them, therefore, they are of minimal help. If your thyroid is being destroyed by antibodies, nothing will regulate it back to normal; you can only take prescription medication to replace the hormones your thyroid does not produce. This is a very treatable issue.
It would be most helpful if you would post whatever thyroid labs were done, along with results and reference ranges - reference ranges vary from lab to lab, so must come from your own lab report. If your doctor did not provide you with a copy of your report, s/he's obligated to do so, upon request.
Once you post your actual lab results, with reference ranges, members will be able to comment more fully on your particular situation.
Hey Valerie,
I'm not a doctor but I do have hypothyroidism. If your blood work came back and said you have an underactive thyroid the doctor should have prescribed you some type of synthroid or thyroid replacement. I dont think it would hurt to have an ultrasound just to make sure but the task is going to be getting the doctor to agree to it. They seem to do the bare minimum these days. Keep us posted on the outcome