Head and Neck Lymph Nodes - Thyroid? Allergies?

[Briarb]

I have a question about a relatively tiny lump I found on the front of my neck on my trachea about 1 inch above my breastbone and about 1 inch and under my Adam Apple.  It's in the very center and goes up and down when I swallow.  I'm assuming its a lymph node that is slightly enlarged (about the size of a pea).  I don't want to say swollen because it doesn't hurt at all, it very mobile, and I while I just recently noticed it, I'm inclined to think its been there quite some time.  It almost feels like its a continuation of my adam's apple/larynx (whatever parts make up the anatomy of my throat) - just another bump going down the front of my neck, except Ive learned to identify lymph nodes in recent months.  I also found two, non-symptomatic, lymph nodes in my upper neck, behind the chin a couple inches that are about the size of kidney beans (one lightly smaller than the other), but they've been that way for a long time I'm pretty sure as I noticed them 6 months ago at least.  I only noticed the neck one recently because I've been searching my body left and right for any sort of swollen lymph node and it occurred to me this lump is not part of my throat but rather a lymph node.  Also, based on the fact that it can easily be moved side to side.

I started feeling a little sick off and on about two weeks ago.  Randomly I would get a little fatigued and feel under the weather like I was catching something, but it would go away, usually after I ate something.   I went to my general doctor and he did an full exam on me, feeling for any swollen lymph nodes.  He didn't find any, but I showed him a few really small lymph nodes behind my ear that I had noticed in March, and he confirmed they were a little bigger then the other side, but "not even the size of a pea" and I shouldn't worry about them since they hadn't changed.  He said if I gained a little weight (I've been pretty skinny my whole life), I probably wouldn't notice all these nodes as much.  He ordered a CBC anyway, mostly just to appease me, which came back normal.  He said I was probably coming down with a cold or another infection and that I should just go home and rest.  I did, and felt better all week, until last night, when I found the lump on my neck.  Then today, I felt sick again the way I did last week, for about an hour or so.  

A little off subject, I'm also probably a hypochondriac and have been diagnosed with Generalized Anxiety Disorder, so I tend to make a big deal out of everything.  And since I didn't find this lump on my neck until after the appointment, I'm going back to see him tomorrow so he can look at it.  I'm inclined to believe these are lymph nodes that were once swollen but simply didn't return to their original size completely after the initial infection wore.   None of them strike me as new, they're all non-symptomatic, and they don't seem to be changing, though I suppose I can't be sure about the one on my neck.  I already expect that he'll tell me just to go home and watch the neck lymph node to see if it changes, but my question is, is this good advice or should I seek a second opinion?  I do have a history of terrible seasonal allergies (including a slight, but reoccurring ear ache I can't seem to completely shake this season, though an antibiotic helped) and I always seem to have post nasal drip of some sort no matter the time of year.  My family also has a history of thyroid disorders, including a sister that has graves disease.   Is there a certain test I should request while I'm there?  Could imply allergies be the cause of the node I've been finding?  Could a thyroid disorder cause a single, slightly enlarged, non-symptomatic, lymph node on the front of my neck?