What if these spots have been here for years and just keep getting bigger?

It is concerning: Practically, almost any skin lesion growing in size over time is concerning. You have to be examined by your doctor at least once, and in some cases over period of time to determine the best course of actions or treatment if needed. In some cases you may need skin biopsy to establish diagnosis. Again, it is up to your doctor to decide after your examination done.

Nevus (plural=nevi): Moles that remain the same can typically be left alone after getting checked out at least once. But any mole that changes needs to be evaluated by either your family doc or dermatologist. Also, learn abcde of moles (nevi): asymmetry, border, color, diameter & elevation (http://cancer.About.Com/od/skincancermelanoma/p/abcdeskincancer.Htm). If your spot matches any of these, go see your doc.

Need eval: This can't be diagnosed with the information that is available. A history, physical examination & other studies may be needed to determine cause/causes. Once accurately assessed a treatment plan can be developed.