Back hurts with bra on?

When I wear my bra for too long my back starts to ache where the strap is, it feels a little better when the bra is off but not much. It feels better if I get a massage on the part that hurts. It's painful like I've been slumped over for a long time. And if I don't wear a bra for a few days my back hurts again because of my breasts. I'm a 32 DD. Please help