what is normal cause of dull aching in the lower back? nerve? disc? muscluar?

i pulled my lower back doing deads (i no no bad form). i didnt get any sharp pain just an aching which got werse over the space of a week or so. i when to a chiro and he said 2 of my lower vetebre had turned to the left so he corected it and my ligaments in that area were tight and had been pulled, i went back a week l8r and he sed my spine looked ok now, the pain was alot less (also doesnt hurt when o cough or sneeze now).

but now i have a constant dull aching in my lower back area, nothing that stops me moving or too painful, its just annoying cause i can feel its there, and i no if i do deads it will make it werse, im worried about starting squats again.
i stretch my hams,glutes and quads every day cause they are all very tight. but doing this seems to make the aching slightly werse for the rest of the day unless i take iburafen.

the pain is like a dull aching, and i feel a pulling feeling when i lean forward or side to side.

im going to go to a physio for electro theropy which helped alot the last time i had this pain.
i want to start back extensions when i feel i can to strengthen my lower back beofre doing deads again. and every day stretching from now on.

any advice or suggestions? what couldthis dull ache be? pulled muscles? if so how long does something like this take to heal?