I would recommend that you go to see your primary care doctor
about this issue, especially since it seems to be continuing for quite a while without resolution.
One possibility that your doctor will want to rule out is insect or other bites. The sporadic occurence of these spots, together with the fact that they are quite itchy, goes along with this. Bed bugs would be one common cause of bites that appear in this pattern.
Another possibility would be eczema
. In particular, a type of eczema called nummular eczema might cause round, itchy spots that come and go on the skin.
Finally, there is the possibility that this is erythema nodosum, a more rare skin condition which can sometimes be associated with an underlying rheumatological condition like rheumatoid arthritis
. Also, rarely, erythema nodosum can be caused by medications. Depo provera is not typically associated with erythema nodosum, but this would definitely be something to consider if the lesions are consistent with erythema nodosum.
Your doctor will be able to take a look and confirm the diagnosis. If these are bites or eczema, then usually a topical medication will help clear them up. If this is erythema nodosum, then additional medical evaluation for an underlying condition will be needed.