Re: Help! I'm new to this.
Your thyroid cells may still be dying off from the RAI, so that can make you hyper and/or toggle you all over the place. Once your thyroid is totally gone and your meds are adjusted properly, all the crummy effects should stop. Until then, your levels may still fluctuate as thyroid cells are probably still dying off from the RAI.
As for the weight gain, it is to be expected...at least a little. Before your system was abnormally running fast and now, or soon, it will be running correctly. You will most likely not be able to eat like you were when hyper. You will now no longer have that "lightning fast" metabolism you might be used to from being hyper but you should be able to maintain a healthy weight once your levels are good.
Give yourself some time. Once your levels are good, you will be right as rain again. Being ramped up all the time as you were is hard on the body so believe it or not, this is a good thing. I've been told by a few people that used to be hyper is that the hardest thing to get used to is not zipping around all the time like they were on fire, which is a direct result of being hyper. The new, slower, more healthy you will be much better for you in the long run.