I was 5'3" at the time (I gained an inch with spinal surgery

!) and started out at 144. I lost 20 lbs, it took me 4 months - I saw you had 5 months to lose 20 lbs, and I think that is very doable if you are dedicated. I probably would've lost it faster if I didn't have an issue with overindulgence in cashews

.
South beach isn't a fast and easy way of eating (like pre made Jenny Craig, etc), but it is a very realistic and healthy way to eat. You'll learn to prep and find your favorite recipes. I would make a bowl of my favorite salad (like black bean) at the beginning of the week and bring it to lunch all week to save time; breakfast casseroles and reheat it in the toaster oven all week; and I LOVE soups so in cooler weather I would make a pot and have that. Lots of crock pot meals as well (chili!! creamy Mexican crock pot is Jennifer and my fav!) too.
Good luck in your journey! Join us on the daily thread and ask as many questions as you'd like.