When should I start working out again after I pulled a muscle in my lower back?

I pulled it last Monday night, after taking a turbo Kickboxing cl. I went to my family doctor Tuesday and he gave me some muscle relaxers, so i am not hurting anymore until right before I go to bed. When I lay down at night, I use a heating pad when i try to go to sleep and it eases it a lot! I am just really wanting to get back to the gym, but not too soon, I don't want to have that pain again!!!