It's your choice whether to wait or not, but what exactly is the rush? If you do have hyperthyroidism, you will have to discuss a treatment (there are three that I know of), then have the treatment and then make sure your T3, T4 and TSH levels are normal again before you try to conceive again. Does this not at least make sense to you?
If you choose the medication route of treatment, there are a couple of kinds of meds, the right med that will work for you has to be found, and the dosage has to be regulated (sort of trial and error) and regular blood drawn to check the thyroid levels to get them back to normal. Again, this takes time and you should not risk getting pregnant during this time until you are stablized for a period of time. Is there some reason you cannot wait a few months at least?
If indeed you have hyperthyroidism, you will need to wait to get that under control before you conceive again. And in the case of one of the treatments, you should not be pregnant while undergoing it (if you choose that treatment) because it involves radiation. Your meds, if you go that route, will also have to be adjusted (to a higher dose) while you are pregnant. I am sure the endocrinologist will tell you exactly what I am saying here when you see him/her. Also, the meds do not work on everyone. If they don't (and again, only time will tell) then you have to opt for one of the other two treatments. (surgery or radiation) The endocrinologist may even decide that he wants an exact image of your thyroid before giving you any treatment and this also involves radioactive dye. I happen to know what I am talking about in regards to this subject, btw.
So seriously, you should get all of this sorted out before you conceive again. It makes no sense not to wait a few months at the very least. There is a huge difference in waiting a few months and "forever".
They didn't recommend waiting before, but that was before this current/recent diagnosis, so that really has no relevance now.