In my opinion...someone who is 158 is not a candidate for weight loss prescriptions. You have totally lost 62 pounds on your own!!!!!!! I don't believe that a "good" doctor will hand out weight loss prescriptions to those who only have 10-20 pounds to lose. I like to equate doctors with hair stylists, or mechanics, or any other profession. There are a lot of people who graduated from the same college or tech school...but they are NOT all equal. There are good and bad in all professions.
There are a few things to consider-is 140 the best goal weight for your body-or was it just soemthing that sounded good? Some of us are just not meant to be 140, 130, or 115...and our bodies just won't do that. Even if we were 115 when we were 17...if we are now 40 and had 3 kids, then that probably isn't ever going to happen again.
140 pounds can be a totally different thing for every individual, depending on your height, age, shape, and fitness level. There are 140 pound women here who range from a size 3/4 to a size 10 depending on those different factors.
While 158 pounds may be overweight to a 5'1" woman-it may be absolutely perfect for a woman who is 5'7".
You have done the right thing by upping your exercise...but have you changed your diet at all? If you are doing the exact same thing now that you started doing at 220...then this may be the issue. What is your curretn exercise regime, and what is your diet like?