if my body is in starvation mode, how do I know and what do I do?

Hi! I'm a bit new here (okay, so really quite new), and I joined because while I studied abroad, I gained 15-20 pounds. When I got back to college, I decided to try the south beach approach because a friend had a great amount of success with it, but 3.5 weeks later I've only sustained a 1 pound loss. I do aerobics and run (running started 2 weeks ago, aerobics 3).

My concern is that during my first few weeks of SB, I didn't watch my calories and am afraid that I might have dipped below 1200 too often. If my body is now hoarding calories/fat, how do I break it of that habit and reintroduce it to normal metabolism?

eat more.  You need to keep exercising but up your calories.  You might gain a little initially, but once your metabolism is back up, you'll start losing.

Take your total number of calories you set yourself to eat each day and divide that by the number of meals you are going to eat them in.  To raise your metabolism and keep it going, I suggest 5 small meals or snacks.  If you are aiming for 1500 calories a day, then each small meal would be 300 calories which is a perfect amount of food if you think about it.  That will keep your body going all day long.