taking dex, weight problem, just starting soon

i havent really lifted weights much, i mean im in alright shape for my age (21) but i have a bad back and my muscles get soar easy in my mid/lower back, i fractured 4 disks alil over a year ago in my lower back and if i do deads or situps it kills my back the next day, anyways i havent been consistant with my lifting because of work and everything but im going to start a cycle of injectable dex but i wonder if i should start lifting for a month or two or if it is bad for me to start lifting on anabolics right away, i already have the stuff just not sure how i should go about it, its a 9week cycle and another reason i want to start with it is because i am very underweight and want to retain some mass, i only weigh about 130 and im 5'11 you can see my ribs and i eat all the time i just have way to high of a matabalisim and i hate it, i was hoping this would counter that also maybe let me get some weight