The most important question is: how long have you been riding for?

Starting to ride again after a few months, let alone several years, will always result in some butt pain while your muscles acclimate. The extra 50 lbs and fact you haven't been on a bicycle in seven years doesn't help. How long that pain lasts varies, but it can be a couple of weeks before a properly positioned saddle will stop hurting you.

That said, it is also very possible that your fit is off. Futz. Raise and lower you saddle, try different tilts, different positionings of your handlebars. It is also possible that your saddle is too narrow, but as finding a saddle that fits can cost hundreds of dollars (you can never know whether a saddle really works until you've ridden on it for a couple of weeks), that should be a last resort.