While you're waiting for Sqad, I'll remind you that you've got an expert available to advise you (when it comes to choosing the best painkillers during pregnancy) in almost any large supermarket. I refer, of course, to the pharmacist, who knows even more about drugs than doctors do. So why not have a word with a pharmacist, to see if he/she can give you something stronger than you've been taking (but which is still safe in pregnancy).
The NHS website says:
"Ideally, pregnant women shouldn't take ibuprofen unless a doctor recommends and prescribes it.
It's best to tell your GP, pharmacist or health visitor about any medicines you're taking.
Paracetamol is recommended as an alternative to ease short-term pain or reduce a high temperature"
http://www.nhs.uk/conditions/Painkillers-ibuprofen/Pages/Introduction.aspx
The NHS website also has a video about exercises which might help you:
http://www.nhs.uk/video/Pages/sciatica-piriformis-syndrome.aspx