I have started to get small bumps on my lower back. they are painless and contain nothing.?

Lipoma possibly: That area is common for lipomas- completely benign fatty tumors just under the skin. Unless they become painful/enlarged (which might indicate an infection and would need medical treatment)- they do not require any intervention and may go away either fir no reason or dye to weight loss.

Sounds like contact: or irritant dermatitis, but need to see derm to confirm. the differential is quite large so there are many other things it could be