OMG!!!!
I instaled PT yesterday and imported my hand history.
I have a MAJOR leak. I'm still digesting it:

of the ~100$ I lost, 70 were in the BB and 20 in the SB.
How can I be so stupid?
I must have been playing week pairs, drawing or dominated hands from the blinds positions, and I did not even noticed it.
I did not analyze what hands I played, but I will surely do it.

At least now I can see a reason for the problem, and I can act acordingly trying to fix it.

I want to thank you guys for all the excelent advice.
I'll post a hand detail if I can find any patern.