Obesity and micro-penis can be linked in various syndromes including XXY, Lawrence-Biedel-Moon, etc. In addition, there can be the PRESUMPTION of micropenis due to an overlying pannus obscuring the root of the penis.
There is no reliable treatment for micropenis due to a genetic disorder; growth can occur if the patient is hormone deficient. Penile lengthening/thickening procedures are available if a patient is bothered enough to undergo surgery. The aesthetic and functional results are variable. Buyer beware. Further information on causes and treatment should be obtained from your family physician, endocrinologist and/or the current relevant literature. This site, while having many users willing to offer information, is not designed to offer medical information and any such information offered here, especially with regard to treatment, should be taken as anecdotal and not professional medical advice.
I'll move this to the Everybody Forum where it is more appropriate.