Hi and welcome! I too am aiming for a fairly low bmi. Be careful, and be prepared to stop sooner if you have to. Its far more important to be healthy!
I'd recommend going to a dietician or a doctor to see what their opinion is on a healthy weight for you. That way you can be assured that you're being healthy and not setting yourself an unachievable goal
You said you're in need of some help. Could you post an example of what you eat on a day? Maybe we can help see if you're going wrong anywhere