Sorry, we would need more information. Back problems include anything from an ache with no pathology to quadraplegia on a ventilator. The former doesnt effect your ticket, the latter does!!!
But if you just have pain in the lower back and no known pathology, join most other pilots. As long as you have full power in your legs and can get in the seat, regulators are disinterested. Mind you, employers may well be interested in anything that might cause to to take a 'sickie' and like any employer might choose the candidate without such a risk!!
Good luck