well it would be a good idea if a physio has a look at you to start off, things like how your lumbar movement , core muscle strength , neuro dynamics need to be evaluated .
if its purely discogenic then a mckenzie extension ex prog would help you , also a work area evaluation is needed. i personally would not advise ultrsound for 15 minutes !! over the area , though moist heat does help if you have muscle spasm . with mckenzie ,you should on some spinal stabilisation ex prog ,if a physio can mobilise the l5 s1 then you probably will have better results
hope this helps