I have to agree with al the posters here. at 5'6", 158 pounds could be consideered an ideal weight for many people. Has your doctor suggested you lose another 30 pounds? If so, then you might ask him why.
In the last several years, I have learned you should base what you SHOULD weight against several factors besides the scale.
1 - how do you look in your clothes? are you just trying to get rid of a little fat roll? then do some core exercises.
2 - are you already exercising 3-4 days a week, 30 minutes a day? maybe you just need to tone up.
3 - if you are not saying yes to any of the suggestions made here, try one of the "Offical" spark teams here and get more answers.
I have hypothyroidism and have struggled the last 5 years to lose the 60+ pounds I Have needed to lose. it goes on and off. Weight watchers worked for a while.
Currently I seem to be having good luck with nutrisystem which is a low glycemic index eating plan. You might want to research new eating plans with your doctor or a nutritionist. THere are many spark teams dealing with either of these eating plans you can join or just go visit and se what informatoin is available. Since I don't know much about you. It is difficult to give you a good plan of attack.
Good luck, and please feel free to spmail me if you would like furhter informaoitn from me.!