Hi, here are a couple things I suggest to my ladies:
Firstly, start now correcting your posture. Stand, tail tucked in, back straight, tummy (if you can in) and shoulders back. Best way to start practicing is against a wall.
Not sure if these exercise will make sense but you can try the following: cat stretches: position yourself on all fours, on the inhale, arch yor back like a cat, head down and then exhale going back to neutral position,
pelvic tilts: lie flat on the floor, legs bent at knees - on the exhale lift your pelvis a couple of inches off the floor, hold and release,
spinal twists - you can do this either seated or lying down - cross one leg over the other and turn in the opposite direction.
I would also suggest a swiss ball - it's great for easing lower back ache and building core strength.
Worth looking out a pre-natal pilates dvd in your library or from amazon - full of back strengthening and leg strengthening exercises and good on the pelvic floor ones too. Otherwise an antenatal yoga class at the weekends may be a nice way of relieving the pains caused by the weeklong commute.
Bubbles I'm a commuter too and have been looking for an antenatal yoga or aquanatal class in the evening or weekend and there's nothing near me at all (village near Colchester in Essex). You'd think with the well publicised increase in the birth rate that health centres would be offering us pg ladies lots of classes! <<fed up emoticon>>