Chances are it is a lumbar disc bulge given the symptoms and aggravating factors you've described. I'm a physio so naturally I would recommend you see a physiotherapist, preferably one with good training in spinal care. When you are pregnant, you can get all sorts of problems you don't get when not pregnant - but you can also get all the same things everyone else does! Regardless of their profession, I would recommend someone with postgraduate McKenzie training - this can be undertaken by physios, osteos, chiros and dr's.

If you want some recommendations please PM me, I've got a few on a list here!