The patch requires about 5 days to reach therapeutic levels. You are on the lowest dose, and I hope that you get some relief. Pregnancy complicates pain management in that every pain medicine passes through the placenta. You don't want your baby to be getting these medications, so LBP may better be treated with shots instead of pills. Mild doses of opiates during pregnancy are normal. Long term treatment may not be the right choice. Talk this over with your doctor.
I don't understand why pregnancy contraindicates nerve ablation. Perhaps its the anesthesia? Another discussion to have with your pain doc.
Patients is a virture -- it will all come out in the end.