Rear brake adjustments

I replaced front and rear brakes on my 2000 astro about 6 months ago.

I used ceramic pads for the front and regular brake shoes on the rear. My mechanic did the work for me. My problem is that even before I replaced the brakes my rear brakes are constantly going out of adjusment. I asked another mechanic to adjust them for me and he told me that they adjusted automatically by themselves every time a pllied the parking brake. But it seems to me that the front brakes are doing all the stoping and the rears aren't really helping. What can I do to remedy this problem or is it normal and have to be adjusting the rear brakes all the time? Thanks for all your help. :feedback:

rear brakes are to be adjusted bye going in reverse and applying brakes several times not bye setting the parking brakes.