Unusual moles

[Mc2cov]

Hello,  I've always had moles on my body.  Recently,  I've been told I should see a dermatologist.  As I age they seem to appear more and more frequently.  A few years ago,  I developed a 3-4 inch patch of darker skin on my lower back.  This is not concerning to me because i was born with a similar birth mark on the opposite hip, however,  my concerns arose when 20 or so moles decided to populate the darker patch of skin.
Is this something I should be weary of?