There are several ways you can get relief:
a. pump up your abs before exercises like squats and deadlifts. this will take some of the stress off your lower back.
b. do reverse hypers atleast once week, go for high reps, super-strick form, and keep the rest periods short for this particular exercise.
c. you need to work on your lower back endurance, im sure you can dig up an article somewhere on this forum.
d. have you had any previous history of lower-back soreness and/or injury?
e. sometimes, it is a good idea to take a week off, just to see how your back feels without the daily pounding.
f. doing ab exercises regularly is a sound idea indeed. change them everyday, unless you want hypertrophy on your abdomen.
g. if all else fails, see an exercise physio-therapist asap.
h. i hope you wear a belt firmly around your waist during heavy DLs and SQs.