I have also found that my glads in my neck and under my chin swell from time to time for no reason. I started to work out at the gym 3 times a week and noticed this is happening less and less. I really think regular exercise helps.
I have been having the same thing for a while now (I started on levothyroxine in May, but the test results are still not normal)... I find, I think, that they tend to swell up more when I'm very tired (not normal tired - like whole-body-slowed-down exhausted).
I found I had a very long bout of swollen glands myself - I am not sure what the cause was but I have an idea.
I believe at times - when hypothyroid and not in balance with it - the immune system will weaken. Even though you do not show signs of a virus or cold coming on the system has a bug and the lymph glands are reacting with some people
I work at a school and even though I had no signs of a cold - I sure looked swollen in the neck glands and OH were they painful too. Then I started getting the frequent colds (where they come on but don't seem to get worse-- kinda lingers)
I was so upset that something was going on - I had a MRI in the glands for lymphoma. I tested negitive.
It seems in the last few months - since I have found my balance - I do not have the swelling anymore. I just recently had a cold but it was a normal one - it came on and my body fought it off within the usual 10 days.
I had swelling at the beginning - but that is also gone now too.