I started getting black little spots on my back but they don't look like blackhead. What can they be?

Without knowing all of your personal particulars there are a number of different factors involved with skin changes. For example, acne, pregnancy, actinic keratosis or an allergic reaction to medication just to name a few. Here is a link provided which may assist you in determining which best fits your conditions. If you have other concerns it would be beneficial, for your own peace of mind, to schedule a check up with a dermatologist. Hope this helps you.

Skin Changes (http://www.webmd.com/skin-problems-and-treatments/tc/skin-changes-topic-overview):

Hi... I remember having a couple on my back which were quite large and quite painfull if you happen to knock them.
Mine were on the spine, I went to the doctor who told me that it was just a blocked sweat gland, known as a cyst and that I would need it surgically removed if it bothered me too much.

I didn't bother but dealt with it myself...

If you have a lot of these spots it could just be... as you say... blackheads, in which case use a medicated shower gell and have lots of hot as you can stand showers, to open the pores, eventually they should disappear.

If in any doubt go and see your doctor who may perscribe an anticeptic ointment or even anti-biotics if he thinks it is an infection.