You describe 'a very small lump' on your neck just above your collar bone. Although one needs to actually examine the area before arriving at a reasonable clinical impression, I shall try and help you with information that may be of use.

There are various possible causes of the type of 'small lump' you describe. The swelling could be within the skin itself, for example, inflammed or blocked sweat gland (much like acne) however, one of the more important causes is a swollen lymph gland just above the collar bone. This is also known as 'supraclavicular lymph gland'. Lymph glands can swell up due to either infection/infmmation or, in some cases due to more serious conditions such as cancer (as this particular lymphatic chain/gland 'drains' fluid from lungs / bowel / ovaries).

The thyroid gland is more 'centreal' in location, just below the voice box in the middle of the neck but sometimes, a cystic swelling of the thyroid gland can extend lower down the neck, however this seems less likely from your description. You say that the lump is not sore or tender but has it changed or increased in size at all? The fact that you are not losing weight and do not have fever are reassuring. I assume that the '2 doctors' you mention had an opportunity to examine your neck after taking a more detailed history. Did they do any blood tests? 

If you remain concerned that the swelling is not improving, I would suggest you make another appointment with your own GP for a further examination and possible explanation as to what they think the swelling is. As mentioned, everything I have said is based upon a few lines of history and it is essential that a full clinical examination be carried out (with any subsequent investigations such as blood tests etc.) before suggesting possible cause/s.

I do hope that above information is useful to you and again, suggest that you arrange a follow-up appointment with your doctor who will either carry out detailed assessment or may choose to refer you to another specialist for further examination. Best Wishes.