Hi Roxy!
I have two major sports that I have done competitively in my life: skating and swimming.
Swimming is a fantastic form of cardio and sprint training. It burns a heck of a lot of calories per hour, though it isn't the best thing for weight loss alone. You would absolutely want to augment your routine with some weight training. Also, swimming is difficult for those who may not know how to swim properly, proper strokes, etc. I think you would get a fine workout from aqua boxing classes. Swimming laps is difficult and takes practice - I would say take it slow and go easy on yourself. Try the boxing classes - if you enjoy the pool and being there, maybe try an adult swimming class? If you are confident in your swimming skills, practice by swimming one or two laps at a time with rests in between.
My advice is:
1. Use a kick-board when you start out. It's a good way to build muscle and adjust to a new exercise.
2. If you have taken little swimming classes in your life, consider taking some adult classes. Learning proper technique and breathing rythms will actually make swimming easier and more enjoyable.
3. Wear a swimming cap. I know a lot of people think it's dorky, but I don't know what could be more dorky than fried hair!! Get some good goggs, too
HTH! Please feel free to ask if you have any more questions.