Hi there
No probs, Hayley you can start now but obviously take it easy, the best form of exercise for you is swimming, as its non weight bearing and you can do toning exercises whilst in the water, lunges and squats etc (tone those legs up ready for childbirth), also you can do walking, start off at 10 minutes then try adding on a minute each time until your up to 30 minutes, try pumping your arms while doing it, remember to keep cool, try not to overheat and drink plenty of water.
You can also do weight training (not heavy weights where your straining but light weights) or you can use dyno bands (stretch bands), use the gym ball against the wall to do squats and sit on the ball and rotate your pelvic muscles, if you are weight training always get advice from a gym first. If i was you i'd do swimming (with a couple of toning exercises), walking and try aqua yoga or something like that - good luck let me know how you get on.
Remember take it easy and drink plenty of fluids!!!
Sue xx