Hi there!

it sounds like pre-labour to me. things are moving and shaking so to speak. i had similar kind of aches in the 2 weeks leading up to DDs birth (and dont worry about having 2 weeks to go...she came at 38 weeks! ). the period like pain is definately a great sign!

What i did for relief was buy a good heat pack and have DH compress it against my back. i also did some of the movements that we were taught in ante-natal class (ie the hip rocking). you may find that this really helps as these dull back aches are like a 'baby' version of the real deal so the movements recommended are also good for this (hope that makes sense! LOL!).
warm showers directed onto the area also help...or going on all fours can help relieve the pressure.

HTH! and good luck!