I get bumps on my legs / back of my arms when my skin gets dry. It's sort of like rough patches with little bumps. Ugh!
A friend told me about a new moisturiser by Neutrogena that is specifically for bumps (rough patches with bumps). I've been using it for about 2 months and it's really helped.
I don't know if yours are also due to dry skin and weird exfoliation (or lack thereof) like mine ... but it might be worth trying out the Neutrogena stuff as it's really inexpensive.
Hope this helps