takes time and it will be difficult at first. but if you get yourself into a routine (usually takes 2-3 weeks) it will be a lot easier to keep up with. and don't push yourself to hard or expect too much at first or you will just get discouraged. if, say during a swim aerobics class, you have to take quite a few breaks, that is okay. you are still working out and pretty soon the number of breaks you have to take will go down.
do you like to workout at home? i would suggest some great yoga dads might be the best way to get back into a routine, 