what is this ??!!!

Been noticing this for a while now and don't know what it is sometimes I can squeeze the substance out which is never really anything it does have something in it but it always seem to come back going to the doctor soon but just wanted to know if anyone out there has ever seen this before? It kind of looks like a small pimple but it is flat doesn't pain really hard to see but its there has a yellowish color.

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